Acne Mechanica

Acne mechanica is an acneiform eruption of papules, pustules and comedones caused by repeated friction, pressure, heat and occlusion of the skin. It appears at the site of contact with equipment or clothing.

It is common in athletes, military personnel and workers who wear helmets, chin straps, shoulder pads, backpacks or tight garments, and in people in plaster casts or braces. It affects adolescents and young adults who are already prone to acne, and develops within 2 to 3 weeks of the new exposure.

Predisposing factors are existing acne, sweating, humid heat and occlusive layers. It often resolves when the friction stops.

Pathophysiology.

Friction and pressure with sweat increase follicular occlusion and rupture, and promote Cutibacterium acnes inflammation. Occlusion hydrates the keratin layer and increases follicular plugging.

• Closed comedones, papules and pustules, and sometimes nodules, strictly localised to the area of pressure or friction.
• Common sites: forehead and chin (helmets and chin straps), shoulders and upper back (pads and backpacks), thighs and buttocks (tight shorts).
• Mild itch or soreness. Scarring is uncommon.

• Clinical diagnosis from the site relating to the equipment and the timing relative to its use.
• Swab for bacteria and culture if pustules persist, or potassium hydroxide microscopy if fungal folliculitis is possible.
• Review of any topical products, sunscreen and occlusive creams.

Differential diagnosis. Acne vulgaris, bacterial folliculitis, Malassezia folliculitis, miliaria, pseudofolliculitis barbae, contact dermatitis and hot tub folliculitis.

• Reduce friction and occlusion: change or pad equipment, use moisture wicking cotton or synthetic layers beneath it, and avoid tight clothing.
• Shower and change clothing soon after sweating and exercise, and wash with a mild non-comedogenic cleanser.
• Benzoyl peroxide 2.5 to 5% once daily (wash or gel), with a topical retinoid (adapalene 0.1%) at night.
• Topical clindamycin 1% with benzoyl peroxide once or twice daily for inflamed lesions, never as monotherapy.
• Oral doxycycline 100 mg daily, or lymecycline 408 mg daily, for 8 to 12 weeks for moderate disease, with a maximum of 3 months in the first course.
• Cleaning of shared equipment.

Monitoring. Review at 8 to 12 weeks.

Referral and escalation. Refer to dermatology if disease is severe, scarring or failing to respond.

Special groups. Avoid tetracyclines in pregnancy and under 12 years, and topical retinoids in pregnancy.