The fluids secreted by the apocrine glands mix with bacteria already present on human skin during heavy sweating, leading to the production of the unpleasant smells associated with strong body odor. Apocrine glands work in tandem with eccrine glands, which produce mostly salt and water, and are most productive when the patient is under emotional pressure or stress.
Apocrine glands are located primarily in the human groin and armpits, the traditional points of emanation for body odor. When the human body becomes overexerted or emotionally upset, its apocrine glands begin secreting and pumping out a milky substance, which has no intrinsic odor of its own.
Once this milky fluid exudes itself onto human skin, bacteria begin to eat and reproduce within it. This process leads to the production of strong odors as the bacteria go through their life cycles and use enzymes to break down the apocrine secretions for ingestion.
Apocrine glands pour their secretions out into hair follicles and tend to develop most densely where hair follicles themselves are dense. This is why they occur in abundance in the armpits and groin and why armpits are so often associated with body odor. The fluid disperses from the hair follicles and onto the skin as more is produced.