Rash on calves every summer may be caused by atopic dermatitis, prickly heat, solar dermatitis and other factors. 1. Allergic dermatitis: the symptoms may be related to allergies, there may be allergens in the summer environment that cause rashes, such as pollen, mosquitoes and other causes of atopic dermatitis resulting in a rash on the calves every summer. 2. prickly heat: the disease is related to the secretion of sweat, sweat duct obstruction and other factors, summer weather is hot, sweat secretion increases, calves may appear prickly heat. 3. Solar dermatitis: the disease is associated with strong sunlight stimulation mostly born in late spring and early summer, calves experience sun exposure, the exposed parts may appear erythema, itching and other symptoms. Every summer calf rash may also be caused by other reasons, it is recommended to go to the hospital in time to identify the cause of the relevant treatment.