When we sweat we smell very bad why.

Question

Sweat itself is virtually odorless to humans; it is the rapid multiplication of bacteria in the presence of sweat and what they do (break sweat down into acids) that eventually causes the unpleasant smell. The smell is perceived as unpleasant, many believe, because most of us have been brought up to dislike it. Body odor is most likely to occur in our feet, groin, armpits, genitals, pubic hair and other hair, belly button, anus, behind the ears, and to some (lesser) extent on the rest of our skin.
Body odor can have a nice and specific smell to the individual, and can be used - especially by dogs and other animals - to identify people. Each person's unique body odor can be influenced by diet, gender, health, and medication.
Two types of acid are commonly present when there is body odor:
Propionic acid (propanoic acid) is commonly found in sweat - propionibacteria break amino acids down into propionic acid. Propionibacteria live in the ducts of the sebaceous glands of adult and adolescent humans. Some people may identify a vinegar-like smell with propionic acid, because it is similar to acetic acid, which gives vinegar its sour taste and pungent smell.
Isovaleric acid (3-methyl butanoic acid) is another source of body odor as a result of actions of the bacteria Staphylococcus epidermidis, which are also present in several strong cheese types.

Sajeev Kumar · Accepted Answer

Sweat itself is virtually odorless to humans; it is the rapid multiplication of bacteria in the presence of sweat and what they do (break sweat down into acids) that eventually causes the unpleasant smell. The smell is perceived as unpleasant, many believe, because most of us have been brought up to dislike it. Body odor is most likely to occur in our feet, groin, armpits, genitals, pubic hair and other hair, belly button, anus, behind the ears, and to some (lesser) extent on the rest of our skin.
Body odor can have a nice and specific smell to the individual, and can be used - especially by dogs and other animals - to identify people. Each person's unique body odor can be influenced by diet, gender, health, and medication.
Two types of acid are commonly present when there is body odor:
Propionic acid (propanoic acid) is commonly found in sweat - propionibacteria break amino acids down into propionic acid. Propionibacteria live in the ducts of the sebaceous glands of adult and adolescent humans. Some people may identify a vinegar-like smell with propionic acid, because it is similar to acetic acid, which gives vinegar its sour taste and pungent smell.
Isovaleric acid (3-methyl butanoic acid) is another source of body odor as a result of actions of the bacteria Staphylococcus epidermidis, which are also present in several strong cheese types.