Body odor can be understood as an unpleasant smell that our body produces when the bacteria that thrive on the skin break down sweat   and release acids. Some people argue that the odor is the bacteria growing on our bodies, but that is not true. Body odor is primarily an outcome of the breakdown of bacteria into certain acids and proteins. It is known as ozochrotia, osmidrosis, or B.O., bromhidrosis.
Let’s look at the reasons for body odor

1. Bacteria
One of the first  reasons for body odor  is bacteria. It thrives in moist environments, such as armpits. So, while sweating, the bacteria break down some proteins found in the sweat into acid. Hence, it is not the bacteria that stinks but rather the bacteria’s by-product which breaks down the sweat, producing body odor.  

2. Eccrine glands
These glands are present across the skin. They are coiled glands and are present in the dermis or the skin’s lower layer. The eccrine glands squeeze the sweat directly onto the skin’s surface via a duct. This sweat has high salt content, making it more challenging for the bacteria to break down. So, body odor from eccrine glands is less likely. 

3. Apocrine glands
Most of the body odor comes from the body’s apocrine glands. They are present in the armpits, eyelids, genital area, breasts, and ears. In the breasts, these glands produce fat droplets in women’s breast milk, and in the ear, they form the earwax. In the eyelids and the skin, these glands are sweat glands. Usually, these glands are found in the nipples, armpits, and groin. They are scent glands and have an odor. 

4. Stress
Another key  reason for body odor  is anxiety and stress, making you sweat more than usual. Some people even have hyperhidrosis, which makes them sweat uncontrollably even without any concrete reason. Often both stress and hyperhidrosis are inter-connected. 

5. Diabetes (diabetic ketoacidosis)
Diabetes is a condition wherein your body does not make adequate insulin or cannot use the insulin it makes. The lack of insulin leads to high blood sugar levels. When the blood sugar levels are high, it might lead to diabetic ketoacidosis. In this condition, ketones build at a dangerous level and are released into the urine and blood. It also makes your breath have a fruity odor. 

6. Menopause, menstruation, and pregnancy
Menopause, menstruation, and pregnancy may lead to hormone fluctuations, which may change the vaginal or body odor in women. It might not necessarily be unpleasant, just slightly different from usual. 

7. Vaginal infections
Certain vaginal infections like bacterial vaginosis or vaginal parasite infection might also cause vaginal odor. A few infections, which occur outside the vagina, might also change the body odor.
The yeast infection in the vagina might not result in any odor, but it may cause a burning or itching sensation. Bacterial vaginosis is the prime cause of vaginal infection in women of childbearing age, and this may produce a fishy odor.
Trichomoniasis, a sexually transmitted infection, might also bring a change in the vaginal odor, and the discharge might smell bad, become frothy, or change color.