Acne Vulgaris : Definition, Pathophysiology, Diagnosis, And Treatments.
- The primary factors involved in the formation of acne lesions are increased sebum production, sloughing of keratinocytes, bacterial growth, and inflammation.
- The primary lesion, the comedo, forms as a result of plugging of the pilosebaceous follicle. The follicular canal widens, and cell production increases. Sebum mixes with excess loose cells in the follicular canal to form a keratinous plug. This appears as an open comedo, or â€œblackheadâ€ (because of melanin accumulation). Inflammation or trauma to the follicle may lead to formation of a closed comedo, or â€œwhitehead.â€ Closed comedones may presage larger, inflammatory lesions.
- If the follicular wall is damaged or ruptured, follicle contents may extrude into the dermis and present as a pustule.
- Increased androgen activity at puberty triggers growth of sebaceous glands and enhanced sebum production. Sebum consists of glycerides, wax esters, squalene, and cholesterol. Glyceride is converted to free fatty acids and glycerol by lipases, which are products of Propionibacterium acnes. Free fatty acids may irritate the follicular wall and cause increased cell turnover and inflammation. P. acnes is a resident anaerobic organism that proliferates in the environment created by the mixture of excessive sebum and keratinocytes. It is antigenic and can increase antibody formation leading to an inflammatory response.
- A primary factor in the development of acne is an alteration in the pattern of keratinization within the follicle. Increased production and sloughing of keratinocytes correlates with comedo formation.
- Surface skin cleansing with soap and water has a relatively small effect on acne because it has minimal impact within follicles.
- Skin scrubbing or excessive face washing does not necessarily open or cleanse pores and may lead to skin irritation.
- use of gentle, nondrying cleansing agents is important to avoid skin irritation and dryness during some acne therapies.
- Benzoyl peroxide may be used to treat superficial inflammatory acne. It is a nonantibiotic antibacterial that is bacteriostatic against P. acnes. It is decomposed on the skin by cysteine, liberating free oxygen radicals that oxidize bacterial proteins. It increases the sloughing rate of epithelial cells and loosens the follicular plug structure, resulting in some degree of comedolytic activity.
- Tretinoin (a retinoid; topical vitamin A acid) is a comedolytic agent that increases cell turnover in the follicular wall and decreases cohesiveness of cells, leading to extrusion of comedones and inhibition of new comedo formation. It also decreases the number of cell layers in the stratum corneum from about 14 to about 5.
- Adapalene (Differin) is a third-generation retinoid with comedolytic, keratolytic, and anti-inflammatory activity. It is available as 0.1% gel, cream, alcoholic solution, and pledgets.
- Tazarotene (Tazorac) is a synthetic acetylenic retinoid that is converted to its active form, tazarotenic acid, after topical application. It is used in the treatment of mild to moderate acne vulgaris and has comedolytic, keratolytic, and anti-inflammatory action.
- Erythromycin with or without zinc is effective against inflammatory acne. Zinc combination products may enhance penetration of erythromycin into the pilosebaceous unit. Commonly used erythromycin formulations include 2% gel, lotion, solution, and disposable pads that are usually applied twice daily.
- Clindamycin inhibits P. acnes and provides comedolytic and anti-inflammatory activity.It is available as 1% or 2% concentrations in gel, lotion, solution, and disposable pad formulations and is usually applied twice daily. Combination with benzoyl peroxide increases efficacy.
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