5 STDs that can cause bruising

Most bruises come from bumping into furniture or overdoing it at the gym. But what if bruises keep appearing without a clear cause?

While uncommon, certain sexually transmitted diseases (STDs) can contribute to unexplained bruising by affecting your platelets, blood vessels, liver function or immune system.

But how does this happen?

A bruise forms when tiny blood vessels beneath the skin are damaged, allowing blood to leak into surrounding tissue. The colour of the skin shifts over time – red or purple at first, then blue-black, greenish-yellow, and finally brown – as your body breaks down the trapped haemoglobin. Most bruises follow obvious minor trauma, like banging your knee against a wall or trapping a finger in a car door.

Sometimes, however, bruises appear more often than expected, in unusual locations, or without any injury. This is where infectious diseases, including a few common STDs, might become something to think about.

Bruising is an uncommon, indirect symptom of a few STDs. Certain STDs can alter your body’s clotting mechanisms or vascular integrity in ways that make bruising more likely.

HIV

Particularly untreated or advanced cases, where immune system impairment are well-documented.

Chronic Hepatitis B and Hepatitis C

Progressive liver damage impairs clotting factor production and reduces platelets.

Rare cases of Gonorrhoea

Disseminated gonococcal infection (DGI) can cause vasculitis and purpuric skin lesions.

It’s worth noting that certain STIs can cause rashes or sores that may appear as bruising.

Before attributing bruises to an STD, you should consider more common explanations. Many of these are straightforward and treatable.

• Age and sex. As you get older, skin thins and capillaries become more fragile, allowing even a small bump to leave a visible mark.
• Medications. Aspirin, NSAIDs (like ibuprofen), warfarin, direct oral anticoagulants, systemic steroids and some antidepressants can all increase bleeding.
• Intense exercise or trauma. Weightlifting, contact sports, or repetitive strain can produce deep muscle contusions that surface as “mystery” bruises days later – especially in areas you wouldn’t normally associate with the activity.
• Nutritional deficiencies. Low vitamin C weakens collagen and makes capillaries fragile (a condition historically called scurvy). Vitamin K deficiency impairs the production of several clotting factors, leading to prolonged bleeding.
• Underlying blood or liver disorders. These can leave you prone to bruising if your clotting system is affected.

HIV, the virus responsible for acquired immunodeficiency syndrome (AIDS), is a common sexually transmitted disease that attacks CD4 immune cells. Without HIV treatment, the virus progressively weakens the immune system, leaving the body vulnerable to opportunistic infections and a range of skin complications.

Bruising during an HIV infection is usually driven by an ineffective immune system. Living with HIV over a long period can weaken your immune response to opportunistic infections, increasing the risk of developing illnesses that might affect the risk of bruising and lowering the body’s platelet count.

Bruising may also be a side effect of some antiretroviral medications, but this side effect is very rare.

Syphilis is a bacterial infection caused by bacteria (Treponema pallidum), often acquired through oral sex, vaginal sexual intercourse, or anal sex.

In secondary Syphilis – typically developing several weeks after the appearance and disappearance of a chancre – a widespread rash appears, but unlike bruising it has typical features:

• Red, copper or brown spots across the trunk, arms and sometimes the palms and soles of the feet.
• Lesions that may be flat (macular) or slightly raised (papular), generally 3–10 mm in diameter.

The rash in secondary Syphilis occurs in roughly 75–90% of untreated infections, with palms and soles affected in about 60% of those cases.

Several features help distinguish the rash from ordinary bruises: lesions are usually symmetric and widespread, non-tender, and not limited to trauma-prone areas. Accompanying features may include fever, weight loss, night sweats, swollen lymph nodes, patchy hair loss and fatigue.

Hepatitis B and Hepatitis C target the liver. Both infections can be passed on through exchanging infected bodily fluids during vaginal, anal, and oral sex. Non-sexual pathways for transmission include:

• Contaminated blood transfusions
• Sharing needles for injecting drugs
• Sharing hygiene items like razors and toothbrushes
• Needle stick injuries
• Unsterilised tattooing or body piercing equipment

Chronic Hepatitis B and C can cause bruising in some people. The damage caused by both infections impairs the liver’s ability to produce clotting factors, which the body needs to control bleeding.

Gonorrhoea is a very common STD affecting the urethra, cervix, rectum and throat. Many people develop mild infections that produce minimal or no obvious symptoms, allowing these infections to spread undetected through unprotected sex with an infected partner.

In typical genital infections, this STD doesn’t cause easy bruising. However, in rare severe systemic complications, bruising becomes possible.

In roughly 0.5–3% of Gonorrhoea cases, Gonorrhoea bacteria enter the bloodstream, causing a disseminated Gonococcal infection (DGI). DGI can sometimes present with a rash with pink and red spots that can rupture and appear like a bruise.

More common Gonorrhoea symptoms include:

• Unusual vaginal discharge or penile discharge
• Burning or pain on urination
• Pelvic or testicular pain
• Pain during sex
• Rectal discomfort or discharge (anal infection)
• Sore throat (oral infection)

Symptoms are more common in those few people who go on to develop DGI, but many Gonorrhoea infections will be silent, with no symptoms at all.

Prolonged untreated infection can cause Pelvic Inflammatory Disease (PID), infertility and chronic pelvic pain, even without bruising. An infected person may also transmit the infection to sexual partners unknowingly if they only have mild symptoms.

Practical prevention strategies:

• Condom use: Consistent and correct use of condoms or dental dams for oral sex, vaginal, and anal sex is one of the most effective barriers. Using condoms reduces STD transmission risk by 70-80%.
• Selectivity with sexual partners: Limiting number of sexual partners and avoiding overlapping partners when possible can reduce exposure. Communicating with partners about STD status is crucial.
• Regular screening: Regular STD testing is recommended every 3-6 months for sexually active individuals.
• Vaccination: Vaccines are available for HPV and Hepatitis B to prevent infections. The HPV vaccine protects against high-risk HPV types that cause cervical and other types of cancer. The hepatitis B vaccine is recommended for infants, healthcare workers, and people with multiple sex partners.

Can an STD be the only reason I’m bruising easily?

It’s actually rare for an STI to be the cause of your bruising. Doctors typically look for multiple contributing factors – medications, alcohol use, age-related skin changes, nutrition, liver disease and inherited bleeding disorders all play a role. HIV, chronic Hepatitis B or C can cause bruising, but it’s uncommon. However, it never hurts to rule out STIs as the cause.

If my STD tests are negative, what should I do about my bruises?

Negative STD results are reassuring, but don’t solve unexplained bruising. Further evaluation with your medical team should be the next step.

How often should I get tested for STDs if I’m worried about bruising and other subtle symptoms?

If you’re sexually active, especially if you have multiple sexual partners, we recommend getting tested once every 3 months. After a known high-risk exposure, you should get tested as soon as possible.

Unusual symptoms can cause a lot of concern. If you’re worried about your sexual health, it’s always a good idea to get tested. Book an STI screen at a sexual health clinic near you by clicking the button below.

This article has been medically reviewed by Dr. Steve Chapman, 20/07/2026.