Quick Answer
STD stands for sexually transmitted disease — an infection passed from one person to another through sexual activity, including vaginal, anal, and oral sex, as well as skin-to-skin genital contact. The term overlaps with STI (sexually transmitted infection), though many prefer STI because 'infection' captures the reality that most cases have no symptoms or 'disease' at all.
- STDs are caused by bacteria (chlamydia, gonorrhea, syphilis), viruses (HIV, herpes, HPV, hepatitis), parasites (trichomoniasis), and ectoparasites (pubic lice, scabies).
- Most STDs are asymptomatic — you can have one and feel perfectly fine.
- Every sexually active person will encounter at least one HPV type in their lifetime (CDC).
- Bacterial STDs are fully curable; viral STDs are manageable but not yet curable.
Context Most Pages Skip
The term 'STD' describes a health outcome (disease), while 'STI' describes the state of being infected whether or not symptoms appear. Since most infections don't produce symptoms, public health shifted toward 'STI' to encourage testing regardless of how people feel.
Why the terminology matters
Words shape behavior: 'disease' implies visible sickness, which discourages asymptomatic testing. 'STI' normalizes the idea that you might carry something without knowing and should test accordingly.
How transmission actually works
Pathogens need entry through mucous membranes (mouth, genitals, rectum) or breaks in skin. Sexual activity provides those routes efficiently, which is why these infections cluster around sexual behavior.
Sources & Further Reading
- CDC — Sexually Transmitted Infections
- CDC STI Treatment Guidelines
- WHO — Sexually transmitted infections fact sheet
- MedlinePlus — Sexually Transmitted Diseases
Figures reflect CDC surveillance and WHO estimates; they are population statistics, not personal risk predictions.