If you have sex with someone who has an infection or disease on their genitals, you can get it, too. Common STDs that might cause you to develop a rash on your penis include:
Scabies. These tiny mites burrow under your skin and lay eggs, causing an acne-like rash and fierce itching. You get scabies by having skin-on-skin contact for an extended period of time with someone who has it. That’s why a common way to get it is through sex. The itching can get worse at night. Scratching the area can lead to sores, which can become infected.
Syphilis. Condyloma lata rash is linked to the secondary stage of this STD. It causes large, raised gray or white lesions on the genitals. You can get it if your penis has direct contact with a syphilis sore (called a chancre) during sex. Chancres don’t itch, so you might not know you have one. Still, syphilis can lead to serious health problems.
Genital herpes may cause ithcing, pain and sores in your genital area. If you have this diease, you may have no obvious signs or symptoms. You can be contagious even if you have no visible sores. There is no cure for genital herpes. But medications can help reduce the symptoms and the risk of spreading the infection to others.