The foul smell from a body specially during a sultry summer is due to the action of ______ on sweat.

The correct answer is bacteria.

Our bodies are constantly producing sweat, especially during hot and humid (sultry) summer days. However, fresh sweat itself is actually nearly odorless. So why does the body smell foul? The answer lies in the microscopic world of bacteria that live on our skin.

Let's break this down step by step:

Step 1 – Understanding Sweat
The human body has two main types of sweat glands:
  • Eccrine glands – found all over the body; produce a watery, mostly odorless sweat that helps regulate temperature.
  • Apocrine glands – found in areas like the armpits and groin; produce a thicker sweat rich in proteins, lipids, and steroids.

Step 2 – Role of Bacteria
The skin naturally hosts millions of bacteria (part of the normal skin flora). When sweat — particularly from apocrine glands — is secreted onto the skin surface, these bacteria get to work immediately. They break down the organic compounds (proteins, fatty acids, and steroids) present in sweat through a process of microbial decomposition.

Step 3 – Production of Odorous Compounds
As bacteria metabolize the sweat components, they produce various volatile organic compounds as byproducts, such as:
  • Short-chain fatty acids (e.g., isovaleric acid)
  • Sulfur-containing compounds
  • Ammonia derivatives
These compounds have a strong, unpleasant smell — which is what we recognize as body odor.

Step 4 – Why Sultry Summer Makes It Worse
During hot and humid weather:
  • The body sweats more profusely, providing a larger food source for bacteria.
  • Warm temperatures accelerate bacterial growth and metabolic activity.
  • Moisture creates an ideal environment for bacteria to thrive on skin surfaces.
All of this combined leads to a significantly stronger and more noticeable foul smell.

Why the other options are incorrect:
  • Melanin – a pigment responsible for skin color; it plays no role in body odor.
  • Moisture – while moisture (humidity) encourages bacterial growth, it is not the direct cause of the foul smell.
  • Virus – viruses do not break down sweat components or produce the volatile compounds responsible for body odor.

Conclusion: The foul smell from the body, especially during sultry summer, is caused by the action of bacteria on sweat. The bacteria decompose the organic molecules in sweat and release volatile, malodorous compounds as metabolic byproducts — resulting in the characteristic body odor.