One cause for an itchy rash on the scrotum is jock itch, a fungal infection, according to the National Center for Biotechnology Information. A second possible cause is dermatitis due to allergic reactions or other conditions.
Jock itch is a type of ringworm. The infection often has a raised ridge near the edges. Doctors generally identify jock itch by sight but may take samples to grow a culture for identification. Keeping the area dry and wearing clean, loose fitting clothes, along with the use of over-the-counter medication twice daily for 10 days usually clears up the infection, but a doctor sometimes writes a prescription for persistent cases.
Contact dermatitis is also a cause of rashes on the scrotum. The skin comes in contact with a variety of materials that have the potential to cause a rash. Clothing dyes, medications and chemicals from the job can cause the rash, according to NCBI.
Some men also have allergic reactions to rubber products used in condoms or nonoxynol, a spermicide that cause the rash, warns NCBI. Topical antibiotics and antiseptics can also cause a reaction.
Scrotal dermatitis can also be related to nutritional deficiencies, such as a lack of magnesium, reports NCBI. Medical conditions, including diabetes, sometimes cause the rash. General dermatological diseases, such as psoriasis, are also sometimes responsible.