Bumps on the scalp can be caused by a skin condition called seborrheic dermatitis. According to the MedlinePlus website, this illness occurs due to the yeast malassezia and an excess production of oil on the skin. Triggers may include stress, infrequent bathing, alcohol-containing lotions and obesity. Red bumps can also be due to a scalp infection called folliculitis. This occurs when the hair follicles become infected by a fungus, virus or bacteria after becoming damaged.