Start odor care
with your armpits and the soles of your feet.
Different causes, different fixes

6 min read

Have you ever smelled yourself?

Most people would probably say yes. But your own body odor can be hard to notice.

This article looks at two important sources of body odor: the armpits and the soles of the feet. Both are places where odor easily arises. But the mechanisms aren't the same.

Putting the research together, genetic differences between individuals are known for the armpits, while for the feet, environmental conditions such as humidity and microbes inside the shoe also matter.

1. Why is it hard to notice your own smell?

According to research on olfactory adaptation (Dalton, 2000), our sense of smell has a property called "adaptation": when we keep smelling the same odor, we become less sensitive to it [1].

Smells that are always close to your body may also become hard to notice because of this property. But that research deals with olfactory adaptation in general, not body odor itself.

Feeling "I'm fine" yourself is not necessarily the same as how others perceive you.

2. The smell isn't sweat itself, but what bacteria break it down into

In the armpits, it has been shown that odor compounds arise when bacteria on the skin use enzymes to break down precursors that have little smell when first secreted [2].

So dealing with odor isn't just "wipe off the sweat." Reduce sweat, curb bacterial activity, wash away the compounds that become odor. Splitting up the causes makes the direction of care easier to see.

3. Armpits: there are genetic differences in odor

Underarm odor varies a lot between people. Part of the reason is genetic.

A single-nucleotide difference in a gene called ABCC11 has been reported to determine whether your earwax is the "wet" type or the "dry" type [3]. This gene's function has also been shown to be involved in forming the typical odor compounds of the armpit [4].

A study of Japanese people also found a strong association between axillary osmidrosis (strong underarm odor) and the wet earwax type [5]. Dry earwax is also known to be common in East Asia.

But you can't say for certain that dry earwax means no odor, or that wet earwax always means strong odor.

How strong your underarm odor is and "whether you're clean" are not the same thing.

Some people wash properly and are still constitutionally prone to underarm odor. Others produce little odor at all.

4. Soles of the feet: sweat, and the environment in your shoes

The hands and feet, including the soles, have a very high density of sweat glands [6]. But having many sweat glands isn't the same as always producing lots of sweat.

What matters for the feet is that they're covered by shoes and socks. Sweat evaporates less, humidity rises, warmth is held in, and it becomes an environment where microbes thrive.

One known cause of foot odor is isovaleric acid. Research has reported how microbes on the feet metabolize components of sweat and other substances to produce odor compounds [7][8].

So with foot odor, you need to look not only at the feet themselves but at the environment inside your shoes.

5. Smell affects how people see you

Disgust is thought to be an adaptive system that evolved to avoid things that could harm the body, such as rotting matter and pathogens [9].

And in an experiment where participants were shown neutral faces while being exposed to pleasant or unpleasant smells too faint to consciously detect, their ratings of how likable the faces were changed [10].

Smell may affect how people see you even before it's clearly noticed as "a bad smell."

6. Armpits and feet call for different approaches

For the armpits, genetic differences and breakdown by skin bacteria matter. For the feet, not just sweating but humidity and the microbial environment in your shoes matter.

Antiperspirants are mainly meant to reduce sweating itself, while deodorants mainly aim to curb bacterial growth and odor [11]. How to read the labels is covered in how to choose an antiperspirant or deodorant.

If the odor is extremely strong, or you sweat so much it interferes with daily life, you also have the option of seeing a dermatologist or other doctor.

7. Not just "wash more," but look at the cause

When you worry about body odor, it's easy to think, "I just need to wash more." Keeping clean matters, of course.

But with the armpits there are genetic differences, and with the feet, humidity and the microbial environment in your shoes play a part.

Where does it smell? Why does it smell?

Once you know the cause, what to do becomes simple.

References