Signs that your rash may be a sexually transmitted infection (STI) include genital discharge or swelling, blisters, pain when peeing, and other symptoms in the anal area. See a doctor for proper diagnosis and treatment.

If you’re worried that you or a partner may have contracted a sexually transmitted infection (STI), read on for the information you need to recognize the symptoms.

Some STIs have no symptoms or only mild ones. If you’re concerned but don’t see symptoms identified here, check with your doctor to discuss your STI risks and appropriate testing.

The Centers for Disease Control and Prevention (CDC) recommends yearly STI testing for most sexually active people.

Different STIs can cause blisters, bumps, or warts to develop on the genitals. The other symptoms you experience, if any, may help determine the cause.

HPV and genital warts

With the human papillomavirus (HPV), the body often naturally clears the virus. However, the body can’t remove all strains of HPV.

The human papillomavirus (HPV) is an STI caused by a virus. Vaccines help prevent many of the strains of HPV that can cause cancer and genital warts. Additionally, even if you are exposed to the virus and develop symptoms, your body can often clear the virus on its own.

Some strains of HPV cause genital warts. The warts can vary in size and appearance. They can look:

  • flat
  • raised
  • large
  • small
  • cauliflower-shaped

If you have bumps that you think may be genital warts, please make an appointment with a doctor. There are many treatments available to help get rid of warts.

A genital wart may appear alone or in a grouping of many in the genital or anal areas.

Herpes

Blisters on or around the genitals, rectum, or mouth may signal a new infection or flare-up of the herpes simplex virus. These blisters break and produce painful sores, which can take several weeks to heal.

Herpes blisters are painful. If the blisters are close to the urethra, urinating may be painful.

It’s important to remember that herpes can still spread from one person to another, even if there are no visible blisters.

Granuloma inguinale

Granuloma inguinale results from a bacterial infection and usually starts with a nodule that erodes into an ulcer. The ulcer is usually painful.

Ulcers from this infection typically take a long time to heal. Early treatment with antibiotics can help prevent scarring.

Syphilis

A single, round, firm, painless sore is the first symptom of syphilis, a bacterial STI. The sore can appear wherever the bacteria enter the body, including the:

  • external genitals
  • vagina
  • anus
  • rectum
  • lips
  • mouth

At first, only one sore may appear, but multiple sores may appear later. The sores are generally painless and often go unnoticed.

Secondary stage syphilis rash and sores

Without treatment, syphilis progresses to a secondary stage. Sores may appear on the mucous membranes of the mouth. They may also appear as widespread skin rashes over the trunk, on the palms, or soles of the feet.

The rash may look red or brown and have a flat or velvety appearance. It usually doesn’t itch.

The rash can also appear on the palms or soles of the feet or as a general rash on the body. Whitish or grayish lesions known as condyloma lata may appear in moist areas in the groin, under the arms, or in the mouth.

Syphilis rashes can have many different presentations, so it’s important to talk with a doctor about testing.

Mpox

While not an STI, mpox can spread through close contact and sexual contact.

After causing flu-like symptoms, mpox can cause a rash that initially looks like pimples or blisters. Over time, the rash may scab and flake off. The bumps may also be painful or itchy.

Mpox may cause additional symptoms, such as:

  • fever
  • chills
  • swollen lymph nodes
  • fatigue
  • muscle aches
  • backache
  • headache
  • respiratory symptoms, such as sore throat, congestion, or cough

Mpox is contagious and usually develops about 21 days after exposure to the virus. To prevent the virus from spreading, a doctor may recommend avoiding close contact with others and wearing a mask.

STIs can cause other symptoms that may occur with or without a rash.

Can STIs cause swollen, painful testicles?

Epididymitis usually occurs due to an STI, like gonorrhea or chlamydia, or a urinary tract infection (UTI).

Epididymitis is the clinical term for pain and swelling in one or both testicles. People with penises who contract chlamydia or gonorrhea may experience this symptom.

Can STIs cause discharge from the vagina?

Small amounts of discharge, especially from the vagina, is often normal.

But some sexually transmitted conditions can cause discharge from the genitals. Depending on the condition, the color, texture, and volume of the discharge may vary:

  • Chlamydia: Though many people with chlamydia don’t have symptoms, this condition sometimes produces a mucus- or pus-like vaginal discharge.
  • Trichomoniasis: With trichomoniasis, or “trich,” vaginal discharge looks frothy or foamy and has a strong, unpleasant odor.
  • Gonorrhea: A yellowish or yellow-green vaginal discharge can be a symptom of gonorrhea, although most people who contract it do not develop symptoms.
  • Pelvic inflammatory disease (PID): If you experience fever or pain along with vaginal discharge, it may indicate PID. It’s best to visit a doctor for treatment.

If you are pregnant or have recently delivered a baby and have new vaginal discharge, especially if it’s green or yellow, and any fever or pain, it’s best to talk with a doctor.

Can STIs cause discharge from the penis?

Some conditions can cause discharge or even bleeding from the penis.

  • Gonorrhea: Gonorrhea produces a white, yellow, or greenish discharge from the penis.
  • Chlamydia: Chlamydia symptoms may include a pus-like discharge from the penis, or the fluid may be watery or milky-looking.
  • Trichomoniasis: Trichomoniasis doesn’t usually show symptoms, but it can cause discharge from the penis in some cases.

Can STIs cause rectal symptoms?

You may also experience rectal symptoms relating to an STI. These symptoms may include:

  • prolonged rectal pain
  • painful bowel movements
  • discharge
  • rectal bleeding
  • itching in the anus

Do STIs cause painful urination?

Many STIs can cause painful urination. Whether you experience this symptom for certain infections can depend on your anatomy.

In people with a vagina, pain, pressure, or burning during or after urination, or more frequent urination, may be a symptom of:

  • chlamydia
  • trichomoniasis
  • gonorrhea
  • HSV

Because gonorrhea in people with a vagina often produces no symptoms or only mild symptoms that can be confused with a bladder infection, it’s important not to ignore painful urination.

In people with a penis, trichomoniasis, HSV, or gonorrhea may cause painful urination. Pain after ejaculation may also occur in those who contract trichomoniasis. Though less common, chlamydia can also cause painful urination.

Many STIs can be treated and cured, especially if diagnosed early.

If you experience any of the above symptoms, see a healthcare professional for a diagnosis and appropriate treatment.

If you have concerning symptoms on your genitals, it’s also best to avoid sexual activity in case the cause may be contagious.

Many infections, including STIs, can cause a rash on the genitals. You can also experience additional symptoms like unusual smells, itching, burning, or warts.

While your symptoms may help you identify the cause, it’s best to talk with a doctor to get an accurate diagnosis and effective treatment.

Some STIs can worsen if not treated quickly.