A human body has millions of sweat glands that can be divided into two types.
Type I, called Eccrine glands, are all over our body, and they secrete water and salt.
Type II, Apocrine glands are found in armpits, breasts, genital area, eyelids, and ears, and they secrete sweat that is full of proteins & fats.
Both types of secretions are fairly odourless, but they provide the much-desired moisture that many bacteria thrive on.
Apocrine glands, which activate at puberty (that is why body odour starts around that time), are particularly attractive to the bacteria because of the proteins and fat.
So, while every square centimetre of our body is covered with thousands of bacteria at any moment, bacteria in our armpits are present in millions per square centimetre.
Since they are present in higher numbers and have access to rich food in Apocrine glands, these locations tend to smell more and stronger than other places.
There are various factors that decide the level and strength of the odour.
Males tend to sweat more and thus, on average, have more frequent smell problems.
Food has also been found to have an impact; e.g., people who eat spicy food tend to have more unpleasant smells.
And then genes also play a role; genes determine what kind of compounds are produced in the sweat.
So two males or two females with the same hygiene levels and food habits can also smell differently based on their genes.
The article is very simple to understand as well as very informative. Keep up the good work and keep sharing such interesting facts.