Feet contain a large number of sweat glands.
But fresh sweat itself is not usually very smelly.
Shoes create a bacterial paradise
Closed shoes trap warmth and moisture.
That creates a humid environment where normal skin bacteria can remain active.
The longer moisture stays trapped, the more opportunity bacteria have to break down sweat-related substances and dead skin.
Bacteria produce the odor
Some bacterial byproducts have strong smells.
One example is isovaleric acid, which has a sharp cheesy odor.
A small amount is enough for the human nose to notice.
Why are some feet smellier?
People differ in sweating, skin microbes, shoe materials, sock choices, and how quickly footwear dries.
Exercise, heat, stress, and hormones can increase sweating too.
How can you reduce foot odor?
The main goal is moisture control.
Wash and dry feet well.
Change damp socks.
Let shoes dry between uses.
Breathable footwear can help.
Is smelly feet the same as athlete’s foot?
No.
Athlete’s foot is a fungal infection.
Ordinary foot odor is usually driven mainly by sweat and bacteria.
They can occur together because both favor warm damp conditions.
This is closely related to why armpits smell, where bacteria also turn otherwise mild secretions into stronger odors.
Your feet make sweat.
Bacteria handle the finishing work.
And that’s the short explanation.
Related explanations: Why do armpits smell?, Why does sweat smell?, and Why do we sweat?