Risks for contracting an STD from someone carrying a virus/bacteria vary a lot.

1.) By [unprotected] sex act, transmission rates are highest for receptive anal intercourse, then receptive vaginal intercourse, then insertive anal, then insertive vaginal, then receptive oral, then insertive oral.

2.) By disease, transmission rates are highest for Gonorrhea and lowest for HIV.

3.) Unprotected oral sex carries very low risks for contracting Trichomoniasis, HIV & Hep B. However, significant risk exist for contracting Gonorrhea,  Chlamydia, Syphilis, HSV and HPV.

4.) Male condoms effectively prevent transmission of STIs like HIV, Hep B, Gonorrhea, Chlamydia, Syphilis and Trichomoniasis.

5.) Male condoms are less effective at preventing skin-born STDS like herpes & HPV, because Herpes & HPV may be present on areas not covered by the condom. Female condoms offer more protection against Herpes & HPV.

6.) For injecting drug users, sterilizing equipment and using a new, sterile needle for each injection will SIGNIFICANTLY reduce your risks of contracting HIV, Hep B or C, or other infections. Chicago Recovery Alliance & Heartland Alliance HIV Prevention Services offer needle exchange and supplies for free at dozens of sites throughout Chicago; and staff can also test for some STIs and help you learn about safer injection and overdose prevention.

Male-to-female (Vaginal) Female-to-male(Vaginal) Receptive Anal Oral Sex (Receptive)
Gonorrhea 50% – Single1 Exposure90% – 2-31 Exposures 20.00% – Single1 Exposure60-80% – Multiple Exposures1 Documented as medium-risk, but no reliable statistics.
Chlamydia 25-40.00% – Single Exposure2,3 25-40% – Single Exposure2,3 Documented as medium-risk, but no reliable statistics.
Syphilis 30.00% 30.00% Documented as medium-risk, but no reliable statistics.
HIV4 1 in 1000 5 in 10,000 1 in 6661 in 2005
Less than 1/10,000
Hepatitis B6 1 in 10-20 1 in 2-4 No documented cases, but risk may exist
1 – New Guidelines for Treating STDs
2 – Victoria von Sadovszky, PhD Nursing
3 – Phillips, John A “Chlamydial Infections” in Current Clinical Practice: Sexually Transmitted Diseases: A Practical Guide for Primary Care

4 HIV Transmission – CDC

5- “STD Basics” San Francisco City Clinic 

6 – Hepatitis B – WHO Factsheet


It’s important to note that certain things can increase or reduce your risks profile:

1.) Having an untreated STI can increase your risk for getting another STI, because they cause lesions (Syphilis, HSV, Chancroid) or irritation (gonnorhea, chlamydia) that compromise your skin’s natural protective barrier. For example, the CDC reports that , individuals are 2-5 times more likely to contract HIV if they have a syphilis lesion and 2-4 times more likely to contract HIV if they have unprotected intercourse during an active herpes outbreak. So besides treating immediate symptoms for less serious STIs, getting prompt care for issues that pop up also helps reduce your risks of being exposed to more “hard-hitters.”

2.) Poor Nutrition, excessive stress, chronic or recurrent infections, chronic stress, certain medications, I.V. drug abuse, and general poor health can all depress your immune system and make you more likely to contract a viral or bacterial infection if you’re exposed. Eating a balanced diet, getting enough sleep, reducing stresses in your life, and not smoking, drinking or using substances, or doing so in moderation, can definitely reduce your risks fr contracting HIV, or any STI.



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