It is usually seen in uncircumcised men due to poor hygiene. Other causes are dermatitis, allergies, infection such as candida, gonorrhea etc,
eczema. Treatment depends upon the cause of the rash, antibacterial or antifungal .ointments can be prescribed by the doctor. It is important to keep the area clean and also to avoid strong soaps or chemicals which can cause a skin reaction.
It is always better to see your doctor who can diagnose and prescribe appropriate treatment for you.