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What is acne?

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Acne (acne vulgaris or common acne) is a dermal inflammatory disease of the pilosebaceous glands caused by a group of unrelated disorders such as lichen planus, folliculitis, herpes zoster, scabies, bad dietary habits, ongoing stress, hormonal disorder, chickenpox and mumps, etc. it is characterized by skin manifestations that range from mild to severe such as redness, comedones (whiteheads), papules, inflamed nodules, pustules, superficial cysts that can be filled with pus, blood or liquids, and less commonly canalizing and deep inflamed purulent sacs may be observed, these sacs arise from dermal inflammation in response to a trigger (infection, allergen, autoimmune disorder, emotional disorder, stress, etc.).

Epidemiology

Acne can affect people of all ages, colors, religions, cultures, races, countries, it can affect the poor as well as the rich and most commonly it affects the girls and boys during puberty. Acne affects about 10% of the world’s global population (affecting about 700 million people). Studies show that females are at higher risk of developing acne than males by nearly 10%.

In the united states alone acne affects about 1/5 of the total population (50-55 million people) while in Australia it affects about 3 to 5 million people.

Pathogenesis

Acne affects mainly the face, chest, back and upper arms, it is caused by a collection of various disorders that often lead to changes in the homeostasis of sebaceous glands, in most cases, this condition usually begins during puberty, when an increase in androgens promotes follicular epithelial differentiation and leads to an increase in the size and activity of pilosebaceous glands.  The presence of an abnormal quantity of keratin in the presence of intrafollicular hyperproliferation leads to intrafollicular hyperkeratosis that leads to blockage of the pilosebaceous follicles and overtime keratin, sebum and allergens or antigens buildup to form whiteheads or comedones; however, in most cases, these comedones are composed of keratin, sebum and propionibacterium acnes (p.acnes) that secrete lipase in the sebum, which is an enzyme responsible for the breaking down of fats into fatty acids and glycerols, thus resulting in breaking down of triglycerides into free fatty acids (ffa), which, in turn, irritates the follicular wall. A hormonal shift and the way it interacts with keratin, sebum and antigens determine the course and severity of acne in most cases.

Chronic exposure to stimulants may lead to overactive sebaceous glands that secrete too much oil to clear through normal pores, this oil combines with dead skin cells forming sticky complex compounds (heterogeneous compounds) that if not wiped properly could lead to blocked follicles or clogged pores. The sebaceous glands continue to secrete oil in response to stimulants, so oils build up beneath the blocked pores creating a fertile broth for the growth of germs and bacteria in and around the pores. Only then skin bacteria can grow fast leading to acne infection, the observance of red and swollen skin can indicate the presence of this infection.

Erythematous macules are red spots or dark spots in dark-skinned people that usually appear in a period ranging from 4 to 6 months after the initial onset and first appearance of acne symptoms, such spots become redder or darker with temperature, when the body temperature rises because of heat or after a physical engagement or exercise; however, these red spots are not scars, neither they are permanent.

Acne cysts are often formed as a result of sebaceous secretions building up in the follicle over time, this building pressure results in dilation of the follicle, which may rupture as a result of building pressure to release free fatty acids, bacterial products, and keratin into the surrounding tissue, which, in turn, induces inflammation and results in an abscess; in most cases, acne usually spontaneously remits, but the time of remission cannot be predicted; however, acne abscesses often heal leaving scars. Acne affects the way our skin repairs itself, and without proper medical intervention, the healing process in skin affected by acne could lead to scars and other complications such as digging or curving in the skin, which can be avoided by proper on-time treatment.

Overtime, untreated acne can lead to skin hypertrophy, which, in turn, can lead to permanent fibrous scars in the affected area (deformed skin), where normal connective tissue and blood organelles are replaced by fibrin and fibrinogen respectively. In this condition, skin acquires the shape of a reddish volcano after losing much of its normal characteristics such as elasticity, regeneration, glandular functions, sensation, precipitation, etc.

Classification by Localization

Superficial acne: is the most common form of acne, it is characterized by clinical signs that range from mild to severe; however, acne is characterized with a very gradual onset, symptoms also may begin as mild changes that worsen gradually, usually, people with acne suffer of whiteheads (closed comedones) and blackheads (open comedones), which may also contribute to or develop into inflamed papules, pustules and superficial cysts. Large cysts are not characteristic, but they may be observed especially after manual manipulation such as scratching or applying wrong drug or after a trauma to an otherwise uninflamed blackhead; the prognosis of superficial acne is good as in most of the cases it heals without leaving scars; however, scratching of ruptured lesions and attempts to extrude superficial cysts may worsen the cosmetic outcomes of superficial acne.

Deep acne: People with deep acne often suffer of symptoms and signs such as deep inflamed nodules and cysts filled with pus or blood that usually develop into abscesses by rupturing; if left untreated, an abscess grows into a pressured abscess that finds its way through the skin surface, where it opens to discharge its contents. The prognosis of Deep acne is relatively good as in most of the cases Lesions and scarring are frequent, Deep acne commonly affects the face, neck, chest, upper two thirds of the back and shoulders.

 

Classification by Lesion Type

Primary skin lesions, primary lesions are manifestations of early-onset acne characterized by acute skin changes that have not yet undergone evolution, which is commonly caused by disease progression or manipulation such as application of a wrong treatment, playing by hands, co infection, low quality hygiene, etc. examples of primary skin lesions include:

Macule is a small, variably shaped, flat and discolored lesion with a size of less than 10 mm whereas large macules whose size is larger than 10 mm are called patches such as flat moles, freckles and rash of viral infections such as rubella, measles, and some drug induced allergic eruptions.

A papule is a small solid lesion whose size is less than 10 mm whereas a plaque is made of a group of papules whose size is greater than 10 mm such as acne, psoriasis, warts, lichen planus, syphilitic chancre, some drug induced allergic eruptions, insect bites, actinic and seborrheic keratoses, and skin cancers.

A nodule is a palpable solid lesion whose size range between 5 and 10 mm whereas nodules larger than 20 mm by size are called tumors such as keratinous cysts, small lipomas, erythema nodosum, fibromas and other neoplasms.

A vesicle is a lesion containing serous fluid whose size is less than 5 mm whereas a blister or bulla is a vesicle whose size is larger than 5 mm. vesicles (bullae) are mainly caused by foreign material irritants, they are characteristic in many diseases and conditions such as in the case of physical trauma, sunburn, insect bites, allergic contact dermatitis or viral infections (herpes, varicella zoster, etc.). Other causes include pemphigus, dermatitis herpetiformis, drug induced eruptions and erythema multiforme.

Pustules are bouncing skin lesions (superficial skin lesions) containing pus or blood. They may result from sero-purulent evolution of vesicles or from an infection or disorder such as acne, folliculitis, furuncles, carbuncles, impetigo and various fungus infections.

Hives or wheals are transient bouncing skin lesions over a localized edema. Hives are often caused by some drug induced allergic eruptions, insect bites, or due to oversensitivity to heat, cold, pressure or sunlight.

Purpura is a medical term used to define a hemorrhagic state affecting the skin and mucous membranes; it is characterized by patches of discoloration due to extravagated blood, which is caused by bleeding into the skin and mucous membranes. Petechiae are small circumscribed reddish-purple spots containing extravagated blood whereas ecchymoses are larger purple-black-bluish confluent areas of extravasation that result from bleeding into the tissues.

Secondary skin lesions, secondary lesions are manifestations of late-onset acne, when primary lesions undergo natural evolution such as a burst vesicle or after a mechanical evolution as in the case of a scratched vesicle. examples of secondary skin lesions include:

Scaling rashes are heaped-up epithelial particles common in patients with seborrheic dermatitis, psoriasis, superficial fungal infections and chronic dermatitis.

Crusts or Scabs are heaped-up particles consisting of dried blood or pus. Crusting occurs in many inflammatory infections.

Erosion is a medical term used to define a condition characterized by focal loss of a part of the epidermis; it is a common condition in many disorders such as acne or herpes simplex. if left untreated, erosions usually transform into ulcers. An Ulcer is a medical term used to define a condition characterized by focal loss of the epidermis and at least part of the dermis, it is common in many disorders and chronic diseases such as bacterial and fungal infections, gastritis, etc. less commonly, ulcers can be caused by a physical trauma or due to an acute bacterial infection where the cause is usually apparent.

Excoriation is a medical term used to define a linear hollowed crusted area caused by mechanical manipulation of the skin such as scratching, rubbing or picking (Excoriated Acne), it is common in many diseases and disorders such as acne, dermatitis as well as in many allergic and viral infections.

Lichenification is a medical term used to define thickened skin area with accentuated skin markings, it is characteristic in many disorders such as Atopic dermatitis and localized scratch dermatitis (lichen simplex chronicus).

Atrophy is a medical term used to define a condition characterized by loose wrinkled skin that can occur normally with aging or as a result of an underlying pathology as in the case of Acne (Atrophic scarring) or Discoid Lupus Erythematosus, or as a result of long-term usage of topical corticosteroids.

Scars are areas where normal skin is replaced by fibrous tissue; scars often develop after an injury or cut, and they may caused by manipulated acne (Acne Scars), by burns and less commonly by other diseases such as Discoid LE.

 

Identification of Acne by Severity

1. Inflammatory acne lesions include papules, nodules, pustules and cysts.
2. Non-inflammatory lesions include comedones (whiteheads) and open or closed blackheads.

 

 

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Verified by: Dr.Diab (January 21, 2017)

Citation: Dr.Diab. (January 21, 2017). Acne Epidemiology Pathogenesis and Classification. Medcoi Journal of Medicine, 10(2). urn:medcoi:article17476.