When STIs do cause symptoms, the most common include unusual or smelly discharge from the penis, vagina or anus; pain or burning when urinating; sores, blisters, ulcers or lumps around the genitals, anus or mouth; itching or irritation; unusual vaginal bleeding (including between periods or after sex); and pain in the lower abdomen or testicles.
Symptoms can appear days to weeks after exposure, and different infections produce different patterns. Because many STIs are silent, the absence of symptoms does not rule out infection - testing is the only reliable way to know.
Seek urgent medical care for red flags such as high fever, severe pelvic pain, severe testicular pain or swelling, or signs of a spreading infection, as these can indicate complications. For any new or persistent genital symptom, see a licensed doctor or sexual-health clinic for diagnosis rather than guessing or self-treating.