Body Fluids & Infection Risk
Some infections spread through blood and specific body fluids (especially during sex or when blood is involved). Knowing which fluids carry risk helps you protect yourself and others.
- Highest risk fluids: blood, semen, vaginal fluids, and (in some cases) breast milk.
- Low-risk fluids: sweat, tears, urine, and vomit—unless blood is present.
- Prevention works: condoms, not sharing needles, and sterile equipment reduce risk greatly.
What are body fluids?
Body fluids are liquids produced by the body (for example: blood, saliva, semen, vaginal fluid, sweat, tears, urine, and vomit). Some infections can be transmitted when a virus or bacteria is present in a fluid and that fluid enters another person’s body (through mucous membranes, broken skin, needles, or sexual contact).
Blood and certain sexual fluids (such as semen and vaginal fluids) can carry viruses that may pass to others. Other fluids like sweat, tears, urine, or vomit are generally low risk for transmitting blood-borne viruses—unless visible blood is present.
Tip: If there is blood on a surface or in a fluid, treat it as potentially infectious and clean it safely.
Protect yourself
- Use condoms correctly (and consistently) for vaginal, anal, and oral sex.
- Do not inject drugs. If you do, never share needles, syringes, or mixing equipment.
- Avoid sharing anything that breaks the skin (tattoo/piercing needles, razors, some home medical devices).
- Choose reputable tattoo/piercing providers who use sterile, single-use equipment.
- Limit alcohol and avoid substances that increase risk-taking.
- Ensure medical/dental equipment is properly sterilized (especially when traveling).
Consider vaccination where appropriate (for example, hepatitis B) and schedule regular STI testing if you’re at risk.
Spread through sexual contact
Many sexually transmitted infections (STIs) spread through contact between mucous membranes and sexual fluids, or through skin-to-skin contact. Common routes include:
- genital-to-genital
- oral-to-genital
- genital-to-anal
Examples of sexually transmitted infections
- Chlamydia
- Genital herpes
- Genital warts (HPV)
- Gonorrhoea
- Hepatitis B
- HIV
- Non-specific urethritis (NSU)
- Pubic lice
- Syphilis
- Trichomoniasis
Some STIs can spread even without visible symptoms—testing and prevention matter.
Infectious diseases in saliva
Saliva can spread some infections—most often through close contact (such as kissing) when viruses are present in the mouth or throat. During contact, microbes can reach the back of the throat and enter the body.
Examples include infectious mononucleosis caused by Epstein–Barr virus (EBV) and infections from cytomegalovirus (CMV), both of which can spread through saliva.
Saliva is not a known route for HIV transmission, and hepatitis C is not typically spread by saliva. Hepatitis B is mainly spread through blood and sexual fluids, but in some situations it may be detected in small amounts in saliva—risk is higher if there are bleeding gums or mouth sores.
This page is for general education and does not replace professional medical advice. If you think you’ve been exposed to an STI or blood-borne infection, seek medical care promptly (especially for time-sensitive prevention options).
Adapted from public health guidance (CDC).