What is the Difference Between an STI and an STD?

The difference between an STI and an STD — sexually transmitted infection and sexually transmitted disease respectively — is challenging to understand, and, in some cases, medical professionals may substitute one term for the other with no distinction between the two. In recent years, some attempts have been made to separate the terms, using STI to designate any colonization of the body with a sexually transmitted illness, whether or not there are symptoms. STD is reserved for when observable symptoms or changes of the body are occurring after infection has taken place.

The definition of the differences between an STI and an STD make "sexually transmitted infection" a broader term than "sexually transmitted disease." The differences mean that anyone who is carrying an asymptomatic or symptomatic sexually spread virus, bacteria or parasite can be classified as having an STI. In contrast, having a sexually transmitted disease means showing some symptoms of the infection and isn’t used when people are asymptomatic.

Such fine distinctions between an STI and an STD may help in understanding sexually transmitted illnesses that could not show symptoms for long time periods. Certain illnesses may be dormant for lengthy times in the body, such as some forms of human papillomavirus (HPV). Alternately, they do not have symptoms that are perceptible without significant examination, though they may be creating an environment of risk for the individual. This last diseaswould actually be classified as an STD because the illness is creating bodily damage, even if that is not perceptible to the person.

It might be best to describe the differences between an STI and an STD as a matter of staging. All STDs begin as STIs because they are all initially asymptomatic, though the period before some illnesses become symptomatic may be quite short. Most STIs become STDs or eventually show some form of symptoms, even if symptoms are only discovered by a doctor and not “felt” by the ill person.

This means that either term may refer to the same group of illnesses and are only differentiated by disease expression. Common diseases that are transmitted sexually and might be called an STI or STD include some of the following:

Genital Herpes
Chlamydia
Gonorrhea
Pubic Lice
Human Papillomavirus
HIV
Syphilis
Trichomoniasis

Understanding the differences between an STI and an STD may be important for people who are sexually active. It is vital to understand that continuing signs of good health and freedom from symptoms doesn’t necessarily mean a person is disease free. People aren’t always able to tell if they or their partners are ill. This would suggest that precautions to practice sex more safely, including limiting the number of sexual partners, is needed to avoid contracting illness.