Infectious Diseases
Sexually Transmitted Infections (STIs)
STIs are common and nothing to be embarrassed about. We provide prompt, confidential care to clear your symptoms and lower complication risks.
Medically reviewed by Dean Blumberg, M.D. on Oct. 02, 2026.
What Is a Sexually Transmitted Infection (STI)?
Sexually transmitted infections (STIs) are diseases that spread through sexual contact. Anyone who is sexually active can get an STI, although certain preventive actions can lower this risk.
There are more than 20 types of STIs. Some of the more common STIs include:
- Chlamydia
- Gonorrhea
- Hepatitis B
- Herpes simplex virus (HSV)
- Human immunodeficiency virus (HIV)
- Human papillomavirus (HPV)
- Syphilis
- Trichomoniasis
If you think you have an STI, turn to the experts at UC Davis Health. We offer testing in clinics close to home. And if you need treatment, we prescribe the most appropriate medication and provide ongoing care for chronic infections.
Our Division of Infectious Diseases is at the leading edge of STI treatment. We’re helping to advance care for HIV and other STIs.
On this page
Symptoms of STIs.
Signs of an STI depend on the infection. Symptoms may be mild or severe. Some STIs don’t cause any noticeable changes.
Common Symptoms
Signs of an STI include:
- Blisters, sores or warts on or near your genitals, anus or mouth
- Discharge from the penis or vagina that may smell bad
- Frequent or painful urination
- Itching, bleeding or pain around the anus
- Painful sex
- Vaginal bleeding
Emergency Symptoms
An undiagnosed or untreated STI can cause severe symptoms that require fast medical attention. Some STIs increase your risk for certain cancers and infertility. Seek prompt medical care if you experience:
- Dizziness or fainting
- Fever and chills
- Severe abdominal or pelvic pain
- Swollen testicles or genitals
Causes and Risk Factors for STIs
Bacteria, viruses and parasites in bodily fluids can cause an STI. STIs are contagious. An infected person can spread the disease through vaginal, oral or anal contact. This includes skin-to-skin contact, penile penetration or penetration with fingers or sex toys. Certain factors increase your risk for an STI.
Multiple Partners
Having sex with more than one person or being intimate with someone who has multiple sex partners (including sex workers), increases risk.
Sharing Needles or Personal Items
Using the same needles for drug injections or tattoos can expose you to infection. This can also happen if you share personal items like razors and toothbrushes.
Unprotected Sex
Engaging in vaginal or anal sex without a condom or oral sex without a dental dam puts you at risk. This risk is lower if you’re in a monogamous relationship.
Diagnosis and Testing for STIs
Our primary care providers offer STI testing, enabling you to get a diagnosis quickly and start treatment for common diseases. Many offices have same- and next-day appointments for urgent symptoms and testing.
Physical Exam
Your provider will learn more about your symptoms and perform a physical exam to look for signs of an STI, such as blisters or discharge.
Blood Tests
A blood test can detect certain STIs, including HIV, hepatitis B and syphilis.
Swab Tests
Your provider uses a swab to collect fluid or cell samples from the genitals or mouth. A lab then checks for STIs, such as chlamydia, gonorrhea, HSV.
Urine Tests
A urine test can detect STIs, such as chlamydia, gonorrhea and trichomoniasis.
STI Treatments
The type of treatment you need depends on the STI. Medications can rid your body of some infections, curing an STI. But viruses that cause HPV, HIV and hepatitis B can stay in your body. These conditions require ongoing care to protect against harmful complications.
Antibiotics
Antibiotics cure many STIs caused by bacteria or parasites, including chlamydia, gonorrhea, syphilis and trichomoniasis. Our nationally recognized infectious disease experts provide the proper type and dose for your diagnosis to protect against antibiotic resistance.
Antivirals
When taken regularly, antiviral medications can keep STIs like HSV, HIV and hepatitis B from getting worse. The medication can reduce herpes outbreaks and lower your risk of spreading HSV to partners. Antivirals for HIV can lower the amount of the virus in your blood to levels so low that you can’t spread the disease to others.
Preventing STIs
Several actions can lower your risk for getting an STI or infecting your partner.
Don’t Share Personal Items and Needles
Don’t share personal items like toothbrushes and razors. Seek help for substance use disorders and don’t share needles. Only go to licensed (regulated) tattoo facilities.
Get Vaccinated
Vaccines help protect against hepatitis B and HPV. Unvaccinated people who are exposed to hepatitis B can lower their infection risk by getting a dose of the vaccine and hepatitis B immune globulin, preferably within 24 hours of exposure.
Practice Safe Sex
Use condoms, dental dams and other protective methods, especially if you have multiple sex partners or are with someone who has sex with different people.
Take Pre-Exposure Prophylaxis (PrEP)
Regularly taking PrEP medication via pills or shots can reduce your chances of getting HIV from sex. When taken as prescribed, PrEP is highly effective for preventing HIV.
As many as
1 in 5Americans has an STI
More than
50%Of new STIs occur in people ages 15 to 24
Sources: Centers for Disease Control and Prevention: Sexually Transmitted Infections Prevalence, Incidence and Cost Estimates in the United States
Office on Women’s Health: Sexually Transmitted Infections
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