There are many causes of dense bumps on the brain, such as acne, chestnut pimples, prickly heat, contact dermatitis, and so on. 1. Acne: androgen secretion is exuberant in the body, the follicle oil secretion increases, Propionibacterium folliculorum infection is related to the follicle sebaceous duct abnormal keratinization hyperplasia. It may cause the appearance of densely packed bumps on the brain. 2. Corns: mainly due to inflammatory stimulation, sweat gland conduit damage, skin damage, manifested as milky white, or yellow, needle to rice grain size pimples, may lead to the brain on the long densely packed pimples. 3. prickly heat: the external temperature is too high caused by excessive sweating, sweat discharge is not smooth, may cause congestion and swelling of the hair follicles, manifested in the brain on the long densely packed pimples. 4. Contact dermatitis: skin contact with external sensitizers caused by the inflammatory reaction, may also lead to the brain on the long dense bumps, accompanied by different degrees of itching and other symptoms. The brain on the long dense small bumps, there may be other reasons, you need to go to the hospital in a timely manner to check, follow the doctor’s instructions for treatment.