Scent masking and scent control

What do skunk-scented body spray, an ozone machine, and activated charcoal have in common? I’ll give you three guesses. Strange as it may seem, all of these items can be used as hunting gear. Add chlorophyll tablets and scent-elimination chewing gum to the list and things start to sound downright weird. Why do hunters use these things? Do I need to use them too?

Welcome to the world of scent control. I hate to be the bearer of bad news, but you stink. Worse still, your scent matters for hunting — a lot.


Humans have an odor that many animals can detect with ease. When it comes to olfaction, or sense of smell, most mammals are veritable superstars compared to us. Even the best camouflage can’t fool a deer getting a nose full of human stink. Yet scent control — the act of minimizing the degree to which your odor gives away your presence when hunting — is easy to overlook. I was guilty of this oversight for most of my first deer season and I paid the price. I hardly saw any deer despite scouring a deer-rich environment.

In this article, I’ll review what we know about how well animals smell and why it matters. I’ll then discuss scent control techniques and offer my advice for scent control newbies.

The Olfactory System
Comparing Sense of Smell in Animals
Scent Reduction
Scent Masking
Hunting the Wind
My Scent Control Advice

Scent Science

The Olfactory System

I began my camouflage review article by discussing the science of animal vision. Now I’d like to do the same with animal olfaction. What exactly are hunters up against? Just how well can animals smell?

Before I go there, let’s talk about what scent is and how we detect it. Aroma compounds, or ‘odorants’, are chemicals that have a tendency to vaporize and float around in the air. There are receptor cells in the nose that detect these floating scent chemicals, which in turn are connected to the nervous system and send the smell signals to the brain. The olfactory system has strong connections to the brain’s fear system and memory system. So, it’s no surprise that hunted animals can quickly learn that human scent = danger.

An aroma compound. These droplets of vapor float around in the air and make contact with our odor receptors in the nose.  Scent control for hunters

An aroma compound. These droplets of vapor float around in the air and make contact with our odor receptors in the nose.

Comparing Sense of Smell in Animals

There are a lot of factors that determine how well any given animal can smell.

One of the most straightforward ways to compare the smelling abilities of different animals is to compare how many scent receptor cells they have. Greater numbers of scent receptors entails greater ability to smell faint odors. In addition, more types of scent receptors entails sensitivity to a wider range of smells.

But even this approach is not as straightforward as we would hope. The olfactory system is complex1. For instance, different animals have different size and shape noses that impact smelling abilities. Additionally, some animals may have more brain processing power dedicated to smelling than others. Complicating the matter further is the fact that many animals have a functioning vomeronasal organ — an additional odor-receptive area in the roof of the mouth2. A vomeronasal organ is almost like a second nose.

For reference, humans have about four hundred types of receptor cells and around 6-10 million total receptor cells in the nose covering 10 square centimeters of space. And unlike most animals, humans do not have a functioning vomeronasal organ.

Unfortunately, there aren’t any scientific studies that take all of the above factors into account to quantify animals’ sense of smell. This makes it very difficult to objectively compare one animal to the next. Compared to animal vision, animal olfaction is very understudied. The vast majority of research has been done in humans and rats, which is not particularly helpful for hunters.

In the sections below, I’ll review the scant information available. As you read, be aware that primary source citations are hard to come by and un-cited numerical estimates of animal smell vary across websites. To be honest, I’m skeptical about the validity of these unreferenced figures. There is a lot we don’t yet understand about how well animals smell in relation to one another.

Scent control whitetail deer

Deer and Other Ungulates

Spend enough time on deer hunting websites or forums and you will undoubtedly see a lot of talk about scent control. Deer are notorious for their excellent sense of smell, so much so that it’s common wisdom that a deer will trust it’s nose more than it trusts it’s eyes and ears to detect danger. The same is usually said about pigs and elk. Ungulates are thought to rely heavily on smell to find food, mate, and survive, using both their noses and vomeronasal organs. Of all classes of animals I discuss in this article, ungulates likely come out on top as expert-level smellers.

Olfactory numbers are hard to come by for most ungulates. As a group, they appear to be grossly understudied in the scientific literature on smell. Deer are often cited as having 297 odor receptor cells and 30% greater smelling abilities than dogs, though I cannot locate the original source of these figures. Recently, the internal structure of a whitetail deer’s nose was characterized in detail. While the nasal cavity may be optimized for ‘sniffing’ in the same way that a dog’s is, the surface area of the olfactory region of the deer’s nose is still unknown.

Predators

Most of the research in canine and feline olfaction has been conducted with domestic dogs and cats. We generally assume that the physiology of dogs and cats is similar to that of their wild relatives. We know that dogs have more types of receptor cells and about 20 times the total number of odor receptor cells compared to humans (dogs have about 220 million). These cells come in 811 different types. Scent-processing also takes up a larger portion of dogs’ brains. Furthermore, the structure of a dog’s nose is much better optimized for smell detection. The act of ‘sniffing’ and the way that air flows through a dog’s nose likely enhances canine sense of smell considerably. Overall, a dog’s olfactory acuity is probably at least 10,000 times better than humans’.

Felines are less talented in the smell department. Despite their small size, domestic cats’ odor receptor cells take up twice the space of humans'(20 square centimeters compared to our 10). But estimates of total odor receptor cells put cats in the 45-80 million range, which is considerably less than canines and ungulates. Compared to canines, bears, and other carnivores, the primary olfactory organ takes up a very small proportion of a cat’s brain.

Of all predators, bears likely have one of the best senses of smell. According to the American Black Bear Association, a bears sense of smell is 7 times greater than a Bloodhound’s. The section of a bear’s nose that is lined with odor receptors is around 100 times larger than ours (1000 square centimeters compared to our 10). However, compared to canines the primary olfactory organ takes up a smaller proportion of a bear’s brain. All told, bears are thought to detect the odor of food from miles away. That’s no small feat.

A moist nose is best for capturing scent molecules floating through the air. Scent control.

A moist nose is best for capturing scent molecules floating through the air.

Rabbits and Hares

Rabbits and hares have better sense of smell than humans, but not as good as canines and ungulates. It is estimated that rabbits have 768 different types of odor cells and 100 million total odor receptor cells. They also use their vomeronasal organ to smell.

Birds

Historically, people believed that birds couldn’t smell. More recent research indicates that birds do have a sense of smell and may use scent to help with foraging, nest-site selection, and breeding. But with these new revelations about avian olfaction, the fact remains that smell is a bird’s weakest sense. Thus far, there is no evidence indicating that birds will ‘spook’ from human scent alone (if they can even detect it in the first place). Current wisdom is that scent control is not important for hunting turkey, waterfowl, or upland birds. It is much more important to disguise yourself visually, as birds have remarkable color vision and superior visual acuity.

And the Winner is…

Comparative animal olfaction is an area where we know relatively little. Unfortunately, much of the information on the internet about game animals’ sense of smell are based on crude estimates or anecdotal evidence. Limited data suggests that bears have the best sense of smell. Ungulates are next — they have similar and probably slightly better olfactory prowess than dogs, who in turn are superior to rabbits and cats. Some degree of scent control should be helpful for hunting each of these animal types. Birds, on the other hand, likely have a weaker sense of smell rely and primarily on vision to detect threats in their environment.


Scent Control

So, if human scent poses a problem for hunting ungulates, predators, and rabbits, what can we do about it? I’ll discuss three types of scent control: 1) Scent Reduction, 2) Scent Masking, and 3) Hunting the Wind.

Do I need scent control to hunt

Scent can travel over great distances, especially in this sort of open country.

Scent Reduction

The goal of scent reduction is to minimize the smell of your body and hunting gear. The absolute ideal would be to smell like nothing at all. Unfortunately, becoming truly scent-free isn’t possible. Odor permeates our existence and even a mild smell turns into a big deal when you’re competing against expert-level olfactory senses.

But remember: hunters have successfully killed wild animals for centuries — and at close range — well before the hunting industry and scent control technology was even invented. Our ancestors lived off the land, they worked, and they sweated. They smelled. It is certainly possible to be a successful hunter without fancy gear.

On the other hand, our distant ancestors didn’t have to worry about smelling like gasoline after filling up their tank on the way to the trail head. They didn’t live in a world full of synthetic fragrances in soap, lotion, makeup, and laundry detergent. The modern American lifestyle is full of strong scents. The good news is that you can reduce your scent by changing a few things in your environment.

Ditch the Smelly Stuff You Lather on Your Body

Start by taking a look at all of your toiletries. Shampoo, body wash, shaving cream, deodorant, mouthwash, hair styling products, laundry detergent, lip balm, and so on. How many of these are unscented? Unless you have known chemical sensitivities or fragrance allergies, I’ll bet nearly all of your hygiene products contain added fragrance. These fragrances can last on skin, hair, and clothing for days and often survive repeated washings with unscented soap. Remember: what smells mild to us will smell very strong to animals with olfactory prowess.

Fortunately, most personal care products come in unscented, fragrance-free variations. You can wear hunter-specific deodorant, wash your hair in hunter-specific shampoo, and launder your clothes in hunter-specific detergent if you want to. Companies are even beginning to produce ‘salon-quality’ beauty products designed for women who hunt. Personally, I don’t use any hunting-specific products, so I can’t make recommendations in that department. As for what I do use, here’s a few examples: soap, lip balm, lotions, and laundry soaps3.

A few simple scent-free options from my arsenal.

A few simple scent-free options from my arsenal.

If you can’t find unscented version of something, first ask yourself if another item you already have can ‘stand in’ for the missing product. For example, I use unscented bar soap for washing my hair and for shaving. If you’re still stuck, ask, ‘Do I really need to use this before I go hunting?’ Items like hair spray can be skipped, if you’re willing. Finally, if you’re planning to switch out your shampoo, soap, or other products for hunting season, I recommended that you start transitioning a couple weeks before you plan to hunt. Synthetic fragrances are persistent and can survive many washings.

Reduce Environmental Contamination

Storage and care of your hunting gear is another area that is easy to target for scent reduction. Store your clean hunting clothing in a way that protects it from picking up smells. Keeping your hunting outfit in the same closet as a bunch of lemon-scented cleaning supplies or in the garage with stinky fertilizer would be a bad idea. Some hunters keep their field clothes in Tupperware containers until they reach their hunting grounds. You don’t want your clothing to pick up the scent of your breakfast sandwich or the local gas station if you can help it.

In addition, if you have a long, hard hike into camp you could wear a different outfit for hiking and keep your hunting clothes in your pack so they don’t get sweaty on the journey. If you will be spending multiple days in the backcountry, consider investing in merino wool layers. Merino wool is a great fabric in general and also has some natural scent control properties. Because it draws moisture away from the skin and evaporates sweat quickly, merino helps keep bacteria that thrive on sweat at bay.

Scent Reduction Sprays, Clothing, and Other Gear

The bad news is that as hard as you try to eliminate all smell, if you’re alive and breathing, you’re still stinking. To counter our inescapable natural odor, a whole industry has cropped up to create and market products that reduce smelliness.

Scent control sprays are a popular option. These sprays help prevent new body odors and/or adsorb existing odors. But that’s not all. You can buy special scent control clothing impregnated with antimicrobial and adsorption technology. Zeolite, activated charcoal, and polymer resin are compounds that are woven into clothing to trap human scent. Scent control technologies extend beyond clothing, too. For example, here’s a chewing gum designed to reduce breath odor. You could even go so far as to hang an ozone machine next to your blind or stand. Petersen’s Bowhunting has a nice article that provides more information about these technologies for scent control.

There’s a lot of debate among hunters about whether scent control products are gimmicky marketing ploys or extremely useful inventions. Even a U.S. District Judge has been forced to weigh in in the case of carbon-based scent control clothing. Hunters’ opinions seem to vary based on personal preference, hunting style, and anecdotal evidence.

In an attempt to collect data more systematically, Field & Stream conducted a number of tests pitting scent control technologies against the nose of a trained police dog. Using a professional canine as a stand-in for a wild deer is highly imperfect for a number of reasons4, but I think it does provide some worthwhile information. From their trials of scent-reduction gear, they found that ozone appeared to slow down the police dog’s positive identification of the hiding person. Scent-elimination sprays, on the other hand, did not. We can’t know for sure how these findings would translate in a true hunting situation, but the results underscore the fact that perfect odor elimination is simply not possible.

Scent Masking

Since becoming scentless is an impossible goal, why not try to fool the animals with a scent disguise? Instead of smelling like a human, you could fly under the radar by smelling like the forest. To try to mask their scent with natural materials, some hunters store their hunting clothing in containers with pine boughs. Others use commercially available cover scents. Parfum of pine tree, anyone? How about acorn cologne or l’eau de skunk? Here are just a couple examples.

There are a few limitations to consider with scent masking. First of all, a cover scent is only likely beneficial if the scent fits with the environment you’re hunting. For example, the apple cover scent would be a terrible fit for desert mule deer hunting. Those deer will never smell apple in their lives. Second, animals are fast learners. One scary experience with an acorn-scented human is enough for an animal to learn that they should be wary of the weird acorn smell. The olfactory, memory, and emotional systems are strongly linked in the brain. Your scent disguise may not last long.

In the Field & Stream police dog test, cover scents did delay the time it took for the trained German Shepherd to positively identify a human hiding in a box. Masking the human scent with something usual, like skunk scent, may have confused the dog a bit. It’s notable that an animal whose job it is to recognize human scent seemed to experience more uncertainty when that scent was combined with fragrances of the forest. More data is needed, but there may be merit to the scent masking technique.

Scent control

Hunting the Wind

Scent is a very mobile entity. Air that is humid and warm transmits scent to animals particularly well, but any breezy day is going to spread scent far across the landscape. If you want to be a successful hunter, you need to familiarize yourself with wind.

Winds are characterized by their speed and the direction they are blowing from. So if you read that there’s a ‘northeast wind’ today, that means that the wind will hit you square in the face when you’re looking northeast. Every location on earth has it’s own prevailing wind — the direction that wind blows the majority of the time. But wind direction can also be quite variable.

Friend or Foe for Scent Control?

Wind can be either the enemy or the friend of the hunter depending on how it’s used. To be honest, learning to use the wind correctly will probably have a bigger impact on your scent control than any of the previous tactics combined. The principle is simple: position yourself and plan your movements in a way that prevents your scent from going where you don’t want it to go. Think about your scent as a bunch of floating molecules and the wind as a flowing stream. Which direction is the wind stream headed? To where will the current carry your scent molecules?

Ideally you want to hike and hunt with the wind in your face. The wind should blow your scent behind you, in the direction you already came from. If you’re able to maintain this orientation, any animal that is in front of you (e.g., upwind) won’t be able to smell you at far range. It doesn’t matter as much if you’re scent lingers behind you, because you’ve already been there. You want to maintain the element of surprise out ahead of you.

When you’re at your hunting location, testing the wind direction is fairly easy. Pick up some dry dirt, fine sand, dry grass, or anything else extremely light and gently toss it into the air in front of you. Watch where it flies. It’s a smart idea to know which way the wind is blowing before you even leave the house, though. If you don’t plan appropriately, you could end up winding (i.e., sending your scent blowing into) the field or draw you wanted to hunt as soon as you leave the car. I recommend choosing your hunting location based on the day’s wind forecast. An accurate weather forecast is invaluable, so make sure you’re checking the closest weather station to your hunting grounds.

Camp location should also be determined by wind direction.

Camp location should also be determined by wind direction.

Thermals and Hunting Strategies

Paying attention to the wind involves more than just checking its direction and acknowledging its presence. It involves frequent monitoring and decision making, taking into account the ways that wind and air movement may be influenced by terrain and temperature change.

Thermals are an excellent example of the terrain and temperature interaction. Perhaps you’ve heard before that warm air rises and cool air falls. This process can create interesting and predictable patters of air movement in mountains and valleys. In the morning, valley air will warm as the sun rises and begin to travel uphill. It’s best to be on a ridge looking into the valley in the early part of the day as the thermals will keep your scent away from the valley floor. In the evening, the pattern reverses as mountain air cools and flows downhill. Check out this article for additional perspective how thermals and prevailing winds can interact. For even more advanced reading, I recommend this article by Gene Wensel.

For the still hunter (e.g., walking very slowly through the landscape looking for game), the best strategy is to always walk into the wind. Keep wandering around and backtracking to a minimum. The less area you stink up, the better. For the tree stand hunter, it may be desirable to have more than one stand location so that you can hunt the spot that is most compatible with wind conditions. You’ll need to approach you stand in a way that doesn’t wind the direction you think the deer will come from. Avoid touching or brushing against plants, trees, and rocks on your way to the stand. Contaminate the landscape as little as possible with your stench.

Spot and stalk hunting is excellent for scent control. In spot and stalk, you’ll make your way to a good vantage point and let your eyes (aided by good binoculars or a spotting scope) do the walking for you. With the right terrain, you can survey large tracts of land without spreading your scent all over the landscape. Choosing the right vantage point is critical, though. It’s important to spot looking into the wind as much as possible. And remember, high ridges make great spotting locations into the valleys and draws below, but work best in the morning when thermals are in your favor.

Once you spot an animal, sit down and strategize. You’ll need to plan your stalk based on terrain features and wind direction. Stalking a game animal involves remaining hidden from your quarry’s eyes and nose. A mild to moderate breezy day can be a real blessing for a spot and stalk hunter, as long as wind direction stays consistent over the course of the day. Shifting or swirling winds are a recipe for a blown stalk. For detailed instruction in spot and stalk strategy, pick up a copy of Dwight Schuh’s book, Hunting Open-Country Mule Deer. It’s worth every penny.

Remember: the wind can be your number one scent control enemy or your number one scent control ally. It all comes down to how to you use it.

My Scent Control Advice

Ultimately, the scent control measures you decide to take should be informed by the types of animals you hunt and the methods you are using to do so.

It’s All About the Wind… and Patience

If you’re a beginning hunter or are thinking about scent control for the first time, I advise you to start simple. Of all the scent control strategies out there, I believe that using the wind properly is the most important and most effective. In perfect wind conditions, I think you could violate all of the scent reduction rules and still execute a successful stalk. If the odorant molecules never travel to the animal’s nose, it doesn’t matter much what you smell like.

But using the wind requires careful attention and discipline. It’s a skill that you’ll acquire with practice. Patience helps, too. In my first year of deer hunting, I knew about all the rules about hunting the wind, but I would accidentally or purposefully violate them if they didn’t agree with my pre-formulated plans for the day. I wondered why I struggled to see deer for weeks on end. You need to be willing to throw your original plans out the window if the wind says so.

I may blend in well enough to fool a mule deer's eyes, but I can't fool a mule deer's nose without some scent control strategy.

I may blend in well enough to fool a mule deer’s eyes, but I can’t fool a mule deer’s nose without some scent control strategy.

Eliminate Unnecessary Scent

Hunters who are particularly vulnerable to the wind (e.g., treestand hunters who are unable to move if the wind shifts, bow hunters who need to get very close to their quarry) should especially consider taking additional scent control measures. Check your hygiene routine and begin reducing or eliminating added fragrances in toiletries. I don’t think it matters much whether you buy scent-free products marketed toward hunters or not. Try a selection of products. Figure out what smells the least and works best with your body. And if substitutes aren’t available or are too pricey, consider skipping out or making your own products (e.g., homemade toothpaste — just leave out the scented oils). Other cheap and simple strategies for scent reduction involve storing your hunting clothes away from any sources of odor. And wearing clothing that wicks moisture away quickly — like merino wool — can help keep body odor to manageable levels.

Scent Control Technology at the Margins

To be fair, I’ve never used fancy scent control products, so I can’t speak to the effectiveness of individual technologies. I think some commercial scent control products may be effective, but aren’t necessary. If you’re using the wind correctly, the added value of scent control technology is likely at the margins. Perhaps you’ll gain a little extra advantage, but it’s hard to say.

More broadly, I encourage you to question the prevailing wisdom that hunters need lots of new and fancy gear to be successful. The cost of gear can be a serious barrier, particularly to new hunters starting from scratch. If you’re on a budget, rest assured — you can successfully kill wild game without scent control technology.

I’d love to hear from you about your olfactory camouflage routine. What scent control measures you use and why?


  1. Number of types of receptor cells does not seem to correlate very well with actual olfactory acuity across different animals. For more on this topic, see here
  2. It’s easy to observe the use of a Jacobson’s organ if you have a pet cat. When approaching a very interesting odor, cats will often open their mouths (called the “Flehman response“), in effect using the roof of their mouth to help them smell. 
  3. I just so happen to have ditched my scented hygiene products well before I started hunting, so what I’ve listed here is simply just a normal part of my everyday routine. Many hunters will alter their grooming routines just before and during the fall hunting season and return to their scented products for the rest of the year. Choose what works best for you. 
  4. For example, a police dog has been trained to seek out human scent and it knows that his job is to find a human as fast as possible. This is a pretty different mindset from a deer who is just moseying along in the forest, unsuspecting of human presence. The police dog also has a small set of locations (in this case, large boxes) where it knows to look for a person, and it knows that a person is going to be in one of them. In addition, he dog was working at very close range and downwind of the boxes, whereas a deer could be a hundred yards away in a typical hunting situation. Finally, it is not clear exactly how a deer’s olfactory system measures up against a German Shepherd’s. If anything, a deer may have more sensitive smelling abilities.