The skin outside the testicles is itchy for several reasons such as hot day sweat stimulation, scrotal skin allergy, contact dermatitis and so on. 1. Hot day sweat stimulation: male patients sweat more in hot days, especially obese patients, and the scrotum is located between the two stocks, sweating, ventilation is not smooth, easy to sweat, sweat will lead to patients with itching symptoms. 2. Scrotal skin allergy: due to the presence of allergens, the formation of itching, flaking, oozing and so on. 3. Contact dermatitis: contact dermatitis is usually caused by the skin and mucous membranes coming into contact with toxic and irritating exogenous substances, which can easily lead to itching, erythema and blisters on the skin. If the patient scratches the affected area and then touches other skin, such as the scrotum, neck and thighs, it is easy to become infected. There may be other reasons for the itchy skin on the outside of the testicles, and prompt medical attention is recommended.