HIV affects the immune system. Testing, appropriate prevention and access to effective treatment are important. Casual everyday contact does not transmit HIV. This overview does not assess an individual exposure or replace time-sensitive professional advice. HIV can spread through infected blood, unprotected sexual contact and from mother to child; ordinary social contact does not spread it. After a possible exposure, seek urgent professional evaluation now because preventive treatment can be time-sensitive. Do not wait for symptoms. A qualified service must assess testing and treatment needs. HealthGuide cannot choose preventive medicines or assess an individual encounter.