What effect shaving has on the development of comedones or acne is unclear.Some skin products might increase comedones by blocking pores, and greasy hair products (such as pomades) can worsen acne. Skin products that claim to not clog pores may be labeled noncomedogenic or nonacnegenic. Make-up and skin products that are oil-free and water-based may be less likely to cause acne. Whether dietary factors or sun exposure make comedones better, worse, or neither is unknown.A hair that does not emerge normally, an ingrown hair, can also block the pore and cause a bulge or lead to infection (causing inflammation and pus).Genes may play a role in the chances of developing acne. Comedones may be more common in some ethnic groups. People of Latino and recent African descent may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation. Pathophysiology
Comedones are associated with the pilosebaceous unit, which includes a hair follicle and sebaceous gland. These units are mostly on the face, neck, upper chest, shoulders, and back. Excess keratin combined with sebum can plug the opening of the follicle. This small plug is called a microcomedo. Androgens increase sebum (oil) production. If sebum continues to build up behind the plug, it can enlarge and form a visible comedo.A comedone may be open to the air ("blackhead") or closed by skin ("whitehead"). Being open to the air causes oxidation, which turns it black. Cutibacterium acnes is the suspected infectious agent in acne. It can proliferate in sebum and cause inflamed pustules (pimples) characteristic of acne.
Laser treatment for acne might reduce comedones, but dermabrasion and laser therapy have also been known to cause scarring.Macrocomedones (1 mm or larger) can be removed by a dermatologist using surgical instruments or cauterized with a device that uses light. The acne drug isotretinoin can cause severe flare-ups of macrocomedones, so dermatologists recommend removal before starting the drug and during treatment.Some research suggests that the common acne medications retinoids and azelaic acid are beneficial and do not cause increased pigmentation of the skin. If using a retinoid, sunscreen is recommended. Rare conditions
Favre–Racouchot syndrome occurs in sun-damaged skin and includes open and closed comedones.Nevus comedonicus or comedo nevus is a benign hamartoma (birthmark) of the pilosebaceous unit around the oil-producing gland in the skin. It has widened open hair follicles with dark keratin plugs that resemble comedones, but they are not actually comedones.Dowling–Degos disease is a genetic pigment disorder that includes comedo-like lesions and scars.Familial dyskeratotic comedones are a rare autosomal-dominant genetic condition, with keratotic (tough) papules and comedo-like lesions. References
External links

Rines, George Edwin, ed. (1920). "Comedones" . Encyclopedia Americana. What causes blackheads, Treatment and Prevention Archived 2020-01-27 at the Wayback Machine