Just like with pimples on other areas of the body, ear pimples form when excess oil is mixed with dead skin cells, according to WebMD. The oil and dead skin cells plug the pores in the ear and bacteria grows, causing swelling, infection and pus.
Pimples are caused by a combination of the oil production, clogged pores, bacteria and dead skin cells, notes Mayo Clinic. Although the shoulders, face, neck, chest and back are more at risk for pimples to form than the ears, hair follicles can become plugged with dead skin cells and oil in the ear, causing acne.
Environmental and personal factors may trigger pimples to form, according to Mayo Clinic. For example, an increase in hormone production, typically in boys and girls during puberty, can cause sebaceous glands to enlarge and increase sebum production. Pregnancy and the use of oral contraceptives may also increase sebum production, which may cause pimples to form or acne to worsen.
Stress may trigger pimples to form in some individuals, and dietary choices, such as dairy products and carbohydrates, may cause acne to form, explains Mayo Clinic. Certain medications containing androgens, corticosteroids or lithium may increase the risk for pimples to form.