Forensic serology is the study of bodily fluids. These include blood, semen, saliva, and sweat.

Blood is a thick, red fluid that has white and red blood cells. The white blood cells protect against bacteria and viruses. Red blood cells provides oxygen to the entire body by way of circulation.

Semen in the male ejaculate fluid that is released when a male and their partner have sex. Sperm is also released with the semen, which can impregnate a woman.

Saliva is a fluid excreted from our salivary glands. This usually happens when one smells something good or thinks of something tasty.

Sweat is a fluid excreted from our sweat glands. This ties into fingerprinting, because the oils and sweat that is left behind creates a fingerprint on a surface.

All of these fluids and other fluids are studied and examined to determine who the fluid came from and where the person was when the fluid was secreted. This allows the victim or suspect to be traced back to the crime scene or another person.