There are few articles describing the use of comedo extraction in peer-reviewed dermatology journals. Decreased levels of retinoic acid in the skin may contribute to comedo formation. In the skin pores, sebum and keratin can create a hyperkeratotic plug called a comedo. Comedo extraction is a widely used method of treatment for acne vulgaris. A comedo is a clogged hair follicle (pore) in the skin. Comedo mastitis is a very rare form similar to granulomatous mastitis but with tissue necrosis.