Dense small rashes on the chin may be caused by allergies, but also perioral dermatitis and folliculitis. 1. Allergy: a dense rash on the chin may be caused by allergies, patients with food allergies or allergies to ultraviolet light, causing eczema, urticaria, contact dermatitis and other allergic diseases, redness, blisters, pimples and other manifestations, accompanied by itching. 2. Perioral dermatitis: Perioral dermatitis can also lead to dense small rashes on the chin, which may be related to the long-term use of glucocorticoid ointment or hormone-containing skin care products. 3. Folliculitis: often caused by bacterial infections, may also be fungal infections, can appear in the chin most of the rice-sized pimples or pustules, pressure has a certain pain. Therefore, the chin dense small rash is not necessarily caused by allergies. There are many other causes of dense chin rashes besides allergy, and patients should consult a doctor in time to clarify the cause of the disease.