A very common STD in both women and men that is caused by a parasite that is passed from one person to another during sexual contact. It also can be passed through contact with damp, moist objects such as towels or wet clothing. Symptoms include yellow, green, or gray vaginal discharge (often foamy) with a strong odor; discomfort during sex and when urinating; irritation and itching of the genital area; or lower abdominal pain (rare).