There are a number of common reasons that a man can develop a rash on the penis. It may be the result of a sexually transmitted disease such as chlamydia, herpes, or syphilis. Rashes on the penis are sometimes caused by an allergic reaction to an irritant that comes in contact with the skin there. Infections, from bacteria, fungus, or parasites, are another common problem that frequently lead to penile rash. Men with a chronic condition that causes rash, such as psoriasis or eczema, may find that it tends to affect the penis and the surrounding skin of the groin.
Some of the main causes of penis rashes are sexually transmitted diseases, or STDs. A number of STDs including herpes, genital warts, and chlamydia can all cause rashes along the penis and on the surrounding skin of the groin, as well as sores, blisters, and irritation. Men who suspect their rash is due to an infection contracted during sexual activity should speak to a doctor, as medication or other treatment is typically needed to clear up the issue.
Allergic reactions can also frequently lead to penis rashes. There is a wide variety of irritants that can cause contact dermatitis in the genital area. Chemicals from dyes or detergents used on clothes may be to blame, as can soaps, lotions, or perfumes. Plants such as poison ivy or oak sometimes cause irritation and rash if they come in contact with the penis. Some men are allergic to latex, and therefore may have an allergic reaction from using condoms made of it.
Penis rashes also occur due to infections on the skin. Bacterial infections like impetigo may cause them. Fungal infections such as yeast infections or tinea cruris, also known as jock itch, can also grow easily in this area, particularly if a man wears tight underwear or pants that cause the groin to become hot or damp from perspiration for long periods of time. The parasite scabies can also cause a rash on the penis.
Sometimes ongoing skin conditions tend to cause penis rashes as well. Both eczema and psoriasis can lead to scaly, itchy, irritated areas on the groin, as well as on other parts of the body. Rashes caused by these conditions tend to appear in response to stress, skin irritation, or other triggers, and will then clear up for periods of time before re-occurring.