Sexually Transmitted Infections: Routes, Symptoms, and Testing

Sexually transmitted infections (STIs) are infections that can pass during sexual activity, but each pathogen has its own routes. Some spread through fluids, some through skin contact, and some through blood. It is inaccurate to list blood, breast milk, lymph, and cerebrospinal fluid together and say that every STI is transmitted that way.

Examples of Transmission Routes

• Gonorrhea and chlamydia: sexual fluids and transmission during birth.
• Syphilis, herpes, HPV, and mpox: contact with sores, lesions, or infected skin and mucosa.
• HIV and hepatitis B: sex, blood or shared injection equipment, and parent-to-child transmission in some settings.
• Hepatitis C: mainly blood-borne; sexual transmission can occur but risk depends on context.

Find sexual-health and STI testing services * Prices and free services vary by provider. Please check the details before booking. Find a provider → 04

Why Test Without Symptoms?

Many STIs cause no symptoms, particularly in the throat or rectum. Testing should reflect exposed body sites rather than using urine alone for everyone. Tell the provider which sites were exposed so the correct samples can be taken.

Symptoms That Need Assessment

Sores, lesions, rash, unusual discharge, painful urination, pelvic pain, testicular pain, rectal pain, or unusual bleeding should be assessed. Seek urgent care for severe pain, high fever, pregnancy, or eye or neurological symptoms.

Choose STI testing that fits your situation * Prices and free services vary by provider. Please check the details before booking. View testing locations → 05

Prevention

Use condoms or dental dams, test according to risk, receive HPV and hepatitis B vaccines if eligible, never share injection equipment, and support partner testing and treatment. PrEP prevents HIV, not other STIs.

Verified references

Links and relevance to the article’s main topic were reviewed on 13 August 2026. Each source supports only the scope stated in the original document and does not replace personalised medical, legal, or service advice.

1. CDC: About Sexually Transmitted Infections Accessed 13 August 2026
2. CDC: STI Treatment Guidelines Accessed 13 August 2026