Health information

What Are STIs?

STIs are common, often silent, and many are curable. Testing is the only way to know for sure.

Sexually transmitted infections (STIs) pass from person to person through vaginal, anal, or oral sex. Some can also pass from a mother to her baby during pregnancy or birth.

STIs are very common. Every year, the world sees more than 370 million new cases of four STIs that can be cured: chlamydia, gonorrhea, syphilis, and trichomoniasis.

Key points

• Anyone who is sexually active can get an STI.
• Many STIs can be cured with medicine.
• Others cannot be cured but can be well controlled.

Signs and Symptoms

Many people with an STI feel completely well. If you do have symptoms, see a clinician.

Many people with an STI have no symptoms, so they can pass it on without knowing. For example, most people with genital herpes do not know they have it.

Symptoms can include:

• Unusual discharge from the vagina, penis, or anus
• Pain or burning when you pass urine
• Sores, blisters, bumps, or ulcers on the genitals, anus, or mouth
• Pain in the lower belly, or pain during sex
• Itching or irritation in the genital area
• A rash, fever, or swollen glands

Why Treatment Matters

Untreated STIs can cause lasting harm to you, your partners, and your babies.

If an STI is not treated, it can cause:

• Long-term pelvic pain
• Infertility (trouble getting pregnant)
• Ectopic pregnancy (a pregnancy outside the womb)
• Some cancers (for example, cervical cancer from HPV)
• Problems in pregnancy and harm to newborns
• A higher chance of catching HIV

Common STIs at a Glance

Bacterial and parasite STIs can be cured. Viral STIs can be controlled, and some can be prevented with vaccines.

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Your clinician will choose the right medicine and dose for you.

How to Protect Yourself

Condoms, vaccines, PrEP, and open talk with partners lower your risk.

• Use condoms every time. Latex condoms used correctly every time lower the risk of STIs, including HIV. Birth control pills, implants, and IUDs do not protect against STIs.
• Get vaccinated.
  • HPV vaccine is recommended for everyone aged 9 to 26. Adults up to age 45 may benefit, so ask your clinician.
  • Hepatitis B and hepatitis A vaccines are also recommended.
• Ask about HIV PrEP. PrEP is a medicine (tablets or injection) that is very effective at preventing HIV when used as prescribed.
• Ask about PEP within 72 hours if you may have been exposed to HIV.
• Limit your number of partners and talk openly with partners about testing.
• Choosing not to have sex is the only completely sure way to avoid STIs.

Who Should Get Tested?

Testing is quick and private, and usually needs only urine, a swab, or a blood test.

• Sexually active women under 25: chlamydia and gonorrhea testing at least once a year.
• Everyone aged 13 to 64: at least one HIV test. Repeat testing depends on your risk.
• All adults: at least one hepatitis B and hepatitis C test.
• Pregnant people: HIV, syphilis, and hepatitis B testing early in pregnancy, plus other tests based on risk.
• Men who have sex with men, people with HIV, and people taking PrEP: testing at least once a year, and every 3 to 6 months if at higher risk. Testing may include the throat and rectum.
• Anyone with symptoms, a new partner, or a partner who has an STI.

You can often collect the swab yourself.

If You Are Diagnosed With an STI

Finish your treatment, avoid sex until cleared, tell partners, and get retested.

1. Take all of your medicine, even if you feel better.
2. Do not have sex until treatment is finished. After single-dose treatment, wait 7 days. Also wait until symptoms are gone and partners have been treated.
3. Tell your recent sex partners so they can be tested and treated. Your clinician may give you medicine to pass on to your partner ("expedited partner therapy"). If telling a partner would put you at risk of harm, tell your clinician.
4. Get retested in 3 months. Catching the infection again is common.
5. Get tested for HIV and syphilis if you have chlamydia, gonorrhea, or trichomoniasis.
6. Return for a "test of cure" if your clinician asks. This is needed for gonorrhea in the throat and sometimes in pregnancy.

When to Get Care Quickly, and Your Privacy

Some symptoms need same-day care. STI care is confidential.

Contact a clinician right away if you have:

• Severe pain in your lower belly, or fever with pelvic pain
• A painful, swollen testicle
• Vision changes, hearing loss, severe headache, or a stiff neck when you have a sore or rash
• Any STI symptoms during pregnancy

Your privacy

STI care is confidential. In the United States, teenagers can agree to their own STI testing and treatment in every state.

Getting tested is a normal, responsible part of taking care of your health. Talk with your clinician about any questions.

How Common Is It?

• About 1 in 4 adults on HIV treatment in sub-Saharan Africa is undernourished (pooled prevalence 23.7%) (Seid et al., PLoS One, 2021).
• Undernutrition (BMI below 18.5) has been reported in 38% of people with HIV in Boston, 43% in Salvador, Brazil, and 77% in Iran (Nahaskida et al., PLoS One, 2024).

How HIV Causes Malnutrition

• Eating less: poor appetite, mouth and throat infections such as thrush, nausea from medications, depression, and food insecurity (Duggal et al., Journal of Immunology Research, 2011).
• Absorbing less: HIV damages the gut lining, and chronic diarrhea leads to loss of nutrients, including vitamins A and E (Duggal et al., Journal of Immunology Research, 2011).
• Needing more: energy needs rise by about 10% without symptoms, 20–30% with symptoms, and about 30% during recovery (Bantie et al., Scientific Reports, 2024).
• Inflammation: chemical signals of inflammation, such as TNF-α and IL-6, drive muscle breakdown and wasting (Bedimo et al., Clinical Infectious Diseases, 2024).

How Malnutrition Harms People With HIV

• Weaker immunity and faster progression to AIDS (Rezazadeh et al., Journal of Health, Population and Nutrition, 2023).
• More opportunistic infections, and they appear sooner: on average about 17 months in underweight patients versus 26 months in well-nourished patients (Assefa et al., PLoS One, 2022).
• About twice the risk of death (Bantie et al., Scientific Reports, 2024).
• Poorer treatment results: more people stop treatment, are lost to follow-up, or respond poorly to HIV medicines (Nahaskida et al., PLoS One, 2024; Assefa et al., PLoS One, 2022).
• Undernutrition during treatment is linked to CD4 counts staying low and to virologic failure (Benzekri et al., BMC Public Health, 2021).
• Missing vitamins and minerals: vitamin A, B12, C, and D, selenium, zinc, and iron are often low (Abdulai et al., PLoS One, 2023).

Warning Signs: Talk to Your Care Team If You Notice

• Weight loss without trying: more than 10%, or more than 5% over 6 months (Nahaskida et al., PLoS One, 2024)
• Loss of appetite, trouble swallowing, or mouth sores
• Diarrhea lasting longer than a month
• Muscle loss, weakness, or tiredness

What Helps

• Take HIV medicines every day. People who keep the virus under control are the ones who regain immune protection and stay well-nourished (Nahaskida et al., PLoS One, 2024).
• Eat a varied diet with protein, carbohydrates, fats, fruits, and vegetables. A less varied diet is linked to being underweight (Assefa et al., PLoS One, 2022).
• Ask for nutrition counseling, supplements, or food assistance if needed (Rezazadeh et al., Journal of Health, Population and Nutrition, 2023).
• Get thrush, diarrhea, nausea, and depression treated early so they do not affect eating.
• Have your weight checked at every visit.

A Hidden Emergency Affecting Billions

Malnutrition means a person's diet has too little, too much, or the wrong balance of energy and nutrients. It covers undernutrition (stunting, wasting, underweight), vitamin and mineral deficiencies, and overweight/obesity (Mphangwe et al., PLOS ONE, 2023).

Every country in the world faces some form of nutrition crisis (Kumar and Mohanty, PLOS ONE, 2022).

The Numbers

• 864 million people went a full day or more without food in the past year, or had to cut back on eating, because they could not afford food (Gallegos, New England Journal of Medicine, 2025)
• 2.33 billion people (almost 3 in 10 worldwide) faced moderate-to-severe food insecurity in 2023 (Gallegos, New England Journal of Medicine, 2025)
• About 45% of deaths in children under 5 are linked to malnutrition (Bayati et al., Journal of Health, Population and Nutrition, 2025)
• Around 149 million children under 5 are stunted, meaning too short for their age (Mphangwe et al., PLOS ONE, 2023)
• 47 million young children were wasted (dangerously thin) in 2019, and 14.3 million of them were severely wasted (Papadopoulou et al., Cochrane Database of Systematic Reviews, 2023)
• 3.1 billion people could not afford a healthy diet in 2020 (Bayati et al., Journal of Health, Population and Nutrition, 2025)

Who Is Most at Risk?

• Young children, especially in the first 1,000 days, from pregnancy to age 2 (Heidkamp et al., The Lancet, 2021)
• Pregnant women and mothers
• Families in low-income countries, where 64.5% of people face food insecurity (Gallegos, New England Journal of Medicine, 2025)
• People affected by conflict, drought, floods, and climate change (Gallegos, New England Journal of Medicine, 2025)
• Older adults, for whom malnutrition leads to frailty, falls, infections, and early death (Dent et al., The Lancet, 2023)

What Causes It?

• Poverty and rising food prices
• Conflict and climate disasters
• Unsafe water, poor sanitation, and repeated infections
• Poor maternal nutrition and limited breastfeeding support
• Limited access to health care and education

(Jama, Scientific Reports, 2025; Gallegos, New England Journal of Medicine, 2025)

Why It Matters

Malnutrition in childhood weakens the immune system, impairs brain development, lowers school performance, and reduces earnings later in life. It also raises the risk of diabetes, high blood pressure, and heart disease in adulthood (Mphangwe et al., PLOS ONE, 2023; Kumar and Mohanty, PLOS ONE, 2022).

Undernutrition can reduce national economic output (GDP) by about 11% in Asia and Africa (Kumar and Mohanty, PLOS ONE, 2022).

The Good News: Solutions Work

• Community-based treatment with ready-to-use therapeutic food allows more than 90% of severely malnourished children without complications to be treated at low cost (Keats et al., The Lancet Child & Adolescent Health, 2021)
• Nutrition in pregnancy and early childhood: micronutrient supplements, breastfeeding support, and fortified foods improve growth (Hussain and Bhutta, Current Opinion in Clinical Nutrition and Metabolic Care, 2026)
• Clean water, sanitation, social protection, and women's empowerment address root causes (Hussain and Bhutta, Current Opinion in Clinical Nutrition and Metabolic Care, 2026)
• Integrated programs that combine health, food, and community support work better than stand-alone efforts (Hussain and Bhutta, Current Opinion in Clinical Nutrition and Metabolic Care, 2026)

The gap: Only about 1 in 3 children with severe wasting receive the treatment they need (Papadopoulou et al., Cochrane Database of Systematic Reviews, 2023).

How You Can Help

• Learn about malnutrition and share this information
• Support organizations that provide food, clean water, and nutrition care
• Advocate for policies that protect mothers, children, and vulnerable communities
• Volunteer with local food banks and community nutrition programs

Good nutrition is a basic human right. Together, we can end malnutrition.