Eczema/Dermatitis: This is often the most common cause of an itching rash on the scrotum. It can be due to irritants, allergens, or atopic predisposition, leading to inflammation and itching.

Tinea Cruris (Jock Itch): A fungal infection that thrives in warm, moist areas of the body, such as the groin and scrotum, causing itching, redness, and a rash.
Psoriasis: Although less common on the scrotum, psoriasis can cause itching, redness, and scaly patches in this area.
Contact Dermatitis: An allergic or irritant reaction to substances like soaps, detergents, or fabrics coming into contact with the scrotum, leading to itching and a rash.
Seborrheic Dermatitis: Can affect the scrotum, causing a red, itchy rash, often accompanied by a scaly appearance.

Scabies: A parasitic infection caused by the mite Sarcoptes scabiei, leading to severe itching, especially at night, and a pimple-like rash. It's contagious and requires prompt treatment.
Syphilis: The secondary stage of syphilis can cause a rash on the scrotum, among other areas, and is critical to diagnose due to its potential for serious complications if left untreated.
Lymphogranuloma Venereum (LGV): A sexually transmitted infection that can cause ulcerative lesions, followed by lymphadenopathy, and if not treated, can lead to serious complications.

Keratosis Pilaris: A condition that causes small, rough patches on the skin, which can occasionally affect the scrotum, leading to itching and dryness.
Lichen Sclerosus: A rare condition that creates patchy, white skin that's thinner than normal, often affecting the genital and anal areas, and can cause itching and discomfort.
Zinc Deficiency: Can lead to skin lesions and itching, including on the scrotum, though this would be part of a broader systemic condition.