Dense small grains on the skin of a 9-month-old baby may be allergies, eczema, and may also be considered to be related to infection, prickly heat and other factors. 1. Allergy: babies in infancy and early childhood have poor physical condition or allergies, and contact with allergens may cause a perverse reaction. This leads to skin allergy symptoms, such as erythema, acne, papules, pimples, and edema, usually accompanied by obvious itching sensation. 2. Eczema: Eczema is related to the joint action of a variety of internal and external factors, with a certain genetic predisposition, leading to inflammatory reactions in the superficial layer of the dermis and epidermis. The main manifestations are localized red companion, itching, papules, papules. 3. Infection: Bacterial and viral infections can cause rash diseases, such as chickenpox and early childhood emergency rash, resulting in a dense red rash on the skin. It is recommended to isolate and treat to avoid infecting others. 4. Prickly heat: baby care in a hot environment, airtight may lead to prickly heat, manifested as dense corn-sized papules, can be accompanied by itching, stinging. To sum up, the appearance of dense small particles on the skin is related to a variety of factors, it is recommended to go to the hospital pediatrics, dermatology, to identify the causes, symptomatic treatment.