Sexually transmitted infections (STIs) can have a range of signs and symptoms, including no symptoms. That's why they may go unnoticed until complications occur or a partner is diagnosed. Signs and symptoms that might indicate an STI include:

• Sores or bumps on the genitals or in the oral or rectal area
• Painful or burning urination
• Discharge from the penis
• Unusual or odd-smelling vaginal discharge
• Unusual vaginal bleeding
• Pain during sex
• Sore, swollen lymph nodes, particularly in the groin but sometimes more widespread
• Lower abdominal pain
• Fever
• Rash over the trunk, hands or feet

Signs and symptoms may appear a few days after exposure, or it may take years before you have any noticeable problems, depending on the organism.

Sexually transmitted infections can be caused by:

• Bacteria (gonorrhea, syphilis, chlamydia)
• Parasites (trichomoniasis)
• Viruses (human papillomavirus, genital herpes, HIV)

Sexual activity plays a role in spreading many other infectious agents, although it's possible to be infected without sexual contact. Examples include the hepatitis A, B and C viruses, shigella, and Giardia intestinalis.

Anyone who is sexually active risks exposure to a sexually transmitted infection to some degree. Factors that may increase that risk include:

• Having unprotected sex. Vaginal or anal penetration by an infected partner who isn't wearing a latex condom significantly increases the risk of getting an STI. Improper or inconsistent use of condoms can also increase your risk.

Oral sex may be less risky, but infections can still be transmitted without a latex condom or dental dam. Dental dams — thin, square pieces of rubber made with latex or silicone — prevent skin-to-skin contact.

• Having sexual contact with multiple partners. The more people you have sexual contact with, the greater your risk. This is true for concurrent partners as well as monogamous consecutive relationships.
• Having a history of STIs. Having one STI makes it much easier for another STI to take hold.
• Anyone forced to have sexual intercourse or sexual activity. Dealing with rape or assault can be difficult, but it's important to be seen as soon as possible. Screening, treatment and emotional support can be offered.
• Abusing alcohol or using recreational drugs. Substance abuse can inhibit your judgment, making you more willing to participate in risky behaviors.
• Injecting drugs. Needle sharing spreads many serious infections, including HIV, hepatitis B and hepatitis C.
• Being young. Half of STIs occur in people between the ages of 15 and 24.
• Men who request prescriptions for drugs to treat erectile dysfunction. Men who ask their doctors for prescriptions for certain drugs — such as sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) — have higher rates of STIs. Be sure you are up to date on safe sex practices if you ask your doctor for one of these medications.

Because many people in the early stages of an STI experience no symptoms, screening for STIs is important in preventing complications.

Possible complications include:

• Pelvic pain
• Pregnancy complications
• Eye inflammation
• Arthritis
• Pelvic inflammatory disease
• Infertility
• Heart disease
• Certain cancers, such as HPV-associated cervical and rectal cancers