Postinflammatory hyperpigmentation (PIH) is a skin condition characterized by the darkening of the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

(

hyperpigmentation Hyperpigmentation, also known as the dark spots or circles on the skin, is the darkening of an area of Human skin, skin or nail (anatomy), nails caused by increased melanin. Causes Hyperpigmentation can be caused by sun damage, inflammation, or ...

) following an inflammatory injury, such as

acne Acne ( ), also known as ''acne vulgaris'', is a long-term Cutaneous condition, skin condition that occurs when Keratinocyte, dead skin cells and Sebum, oil from the skin clog hair follicles. Typical features of the condition include comedo, ...

, dermatitis, infectious disease, or trauma. Less frequently, it may occur as a complication of a medical procedure performed on the skin. It is a common cause of skin discoloration and can affect individuals of all skin types.

Symptoms and signs

PIH manifests as areas of increased pigmentation or darkened skin. The color can range from light brown to deep brown or grey to black. Individuals with darker skin typically develop lesions that are darker and last longer compared to people with lighter skin color. Without any treatment, PIH usually fades in the 6-12 months following its appearance, until it is no longer visible.

Causes

Postinflammatory hyperpigmentation develops after the original symptoms of an inflammatory skin condition disappear. Common triggers include acne lesions, cuts, burns, or skin conditions like

eczema Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened ...

. Additionally, UV sun exposure and

sunburn Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and other animals include red or reddish skin tha ...

are involved in the development, darkening, and expansion of hyperpigmented skin lesions. Some

medical procedure A medical procedure is a course of action intended to achieve a result in the delivery of healthcare. A medical procedure with the intention of determining, measuring, or diagnosis, diagnosing a patient condition or parameter is also called a medi ...

s performed on the skin can cause an inflammatory reaction, which may lead to hyperpigmentation, even if the inflammation itself is temporary. The exact pathogenesis of PIH is poorly understood. It is known to be driven by

cytokine Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...

-mediated

paracrine In cellular biology, paracrine signaling is a form of cell signaling, a type of cellular communication (biology), cellular communication in which a Cell (biology), cell produces a signal to induce changes in nearby cells, altering the behaviour of ...

interactions between

keratinocyte Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referre ...

s and

melanocyte Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the eye (the uvea), the inner ear, vagina ...

s, eventually stimulating the melanocytes to dramatically increase production of

melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

, which then deposits in the skin.

Prevention

Hyperpigmentation can generally be prevented by inhibition of

melanogenesis Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea), the inner ear, vaginal epithelium, meninges, bones, and heart foun ...

, with agents such as 4-Butylresorcinol, while the wound is healing. Notice that such agents might interfere with wound healing.

Diagnosis

A diagnosis of postinflammatory hyperpigmentation is established based upon its clinical presentation coupled with a recent history of inflammation over the same area.

Diagnostic tests A medical test is a medical procedure performed to detect, diagnose, or monitor diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, diagnostic imaging, genetic t ...

are not required, but can rule out some other conditions, such as

Addison's disease Addison's disease, also known as primary adrenal insufficiency, is a rare long-term endocrine disorder characterized by inadequate production of the steroid hormones cortisol and aldosterone by the two outer layers of the cells of the adr ...

systemic lupus erythematosus Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...

. Wood’s lamp evaluation can be used in the diagnosis as well.

Treatment

Treatment for postinflammatory hyperpigmentation may include

topical A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...

agents like

hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. It has two hydroxyl groups bonded to a benzene ring in a ''para' ...

retinoid The retinoids are a class of chemical compounds that are natural derivatives of vitamin A or are chemically related to it. Synthetic retinoids are utilized in cosmetic formulations, clinical dermatology, and the treatment of some forms of cancer ...

ascorbic acid Ascorbic acid is an organic compound with formula , originally called hexuronic acid. It is a white solid, but impure samples can appear yellowish. It dissolves freely in water to give mildly acidic solutions. It is a mild reducing agent. Asco ...

, and

azelaic acid Azelaic acid (AzA), or nonanedioic acid, is an organic compound with the formula HOOC(CH2)7carboxylic acid, COOH. This saturated dicarboxylic acid exists as a white powder. It is found in wheat, rye, and barley. It is a precursor to diverse ind ...

, as well as

chemical peel A chemical peel is a treatment used to improve and smooth the texture of the skin. The skin on the face is most commonly treated, but peels can also be performed on the body. Chemical peels are intended to remove the outermost layers of the skin ...

s or laser therapy to promote skin renewal and reduce pigmentation. Sun protection is also crucial to prevent further darkening of the affected skin. In severe or recurrent cases,

combination therapy In mathematics, a combination is a selection of items from a set that has distinct members, such that the order of selection does not matter (unlike permutations). For example, given three fruits, say an apple, an orange and a pear, there are ...

of hydroquinone plus one or more additional topical agents is common. Topical medications and other non-procedural treatments are preferred over chemical peels, laser therapy,

dermabrasion Dermabrasion is a type of surgical skin planing, generally with the goal of removing acne, scarring and other skin or tissue irregularities, typically performed in a professional medical setting by a dermatologist or plastic surgeon trained spec ...

, and other "destructive therapies". This is because the topical treatments are often very effective in managing PIH and typically cost less, while also having lower potential for

side effect In medicine, a side effect is an effect of the use of a medicinal drug or other treatment, usually adverse but sometimes beneficial, that is unintended. Herbal and traditional medicines also have side effects. A drug or procedure usually use ...

s or worsening of the condition. Some patients (especially those with darker skin) have been known to experience worsening of their PIH with destructive therapy, rather than improvement. The reason for this is often not known.

References