Seborrhoeic dermatitis

Seborrhoeic dermatitis typically appears as oily, yellowish, flaky skin. Although commonly associated with oily skin, it can also appear on dry scalps or skin, where the flaking may look similar to dandruff. The flakes can be fine, loose, and diffuse or thick and adherent. In addition to flaky skin, seborrhoeic dermatitis can have areas of red, rashy, inflamed, and itchy skin that coincide with the area of skin flaking, but not all individuals have this symptom. Individuals with seborrhoeic dermatitis are subject to recurrent bouts and it may be a lifelong condition. Seborrhoeic dermatitis can also occur quickly and severely in patients with Human Immunodeficiency Virus (HIV). This is sometimes the first indication of HIV. ==Causes==

The cause of seborrhoeic dermatitis has not been fully clarified as of 2019. In addition to the presence of Malassezia, genetic, environmental, hormonal, and immune-system factors are necessary for and/or modulate the expression of seborrhoeic dermatitis. The condition may be aggravated by illness, psychological stress, fatigue, sleep deprivation, change of season, and reduced general health. Bacteria Several bacteria, including Propionibacterium species and Staphylococcus aureus, have been shown to have some level of interaction with seborrhoeic dermatitis, though their exact impact is not known. have been correlated with increased risk. Immune dysfunction Those with immunodeficiency (especially infection with HIV) and with neurological disorders that may impact immune system function such as Parkinson's disease (for which the condition is an autonomic sign) and stroke are particularly prone to it. Climate Climate can affect seborrheic dermatitis, but there is a lack of consensus about which climates tend to exacerbate seborrheic dermatitis the most. Some studies show low humidity and low temperature are responsible for the high frequency of seborrheic dermatitis. Others suggest hot environments may also worsen seborrhoeic dermatitis. Dry skin and an impaired skin barrier contribute to the condition. It is likely that climate and weather variations affect the water and lipid content of skin. == Mechanism ==

Seborrhoeic dermatitis is a complex condition with many interacting factors that are not yet fully explained. In general, the major factors that influence the development and severity include Malassezia yeast present on and in the skin, skin production of oily sebum, and a subsequent inflammatory response against Malassezia and their byproducts. Additional factors involved in the condition are a compromised skin barrier, the makeup and amount of sebum produced, the character of the immune response and inflammation, and the presence of other microbe species inhabiting the skin. A suggested series of events leading to seborrhoeic dermatitis is an initially damaged skin barrier and abnormal sebum production, which leads to a change in the microbiome of the skin that in turn elicits an immune response. An alternative explanation is an increase in sebum production feeding an increase in the Malassezia population that instigates inflammation; the inflammation then causes cellular changes that damage the skin barrier. This barrier disruption then encourages additional Malassezia growth and inflammation and again worsens skin barrier function. == Diagnosis ==

Typically, seborrhoeic dermatitis is a clinical diagnosis based on a physician's expertise in identifying and differentiating skin conditions based on the history of the individual and the appearance of the skin. However, seborrhoeic dermatitis may also be diagnosed with additional testing. The least invasive test is a visual inspection in the clinic using a Wood's Lamp. A KOH test can also be used, where skin scraping of the affected skin may also be taken and prepared with potassium hydroxide (KOH) and visualized under a microscope to look for Malassezia or other microbiological cells. Additionally, a fungal culture of the affected skin may be taken to attempt to grow and identify the causative organism. Differential diagnosis Seborrhoeic dermatitis can look similar to other skin conditions that share its characteristic dry, flaky, scaly, and inflamed appearance, but have different causes and treatments. Physicians use the history of the individual with the skin condition as well as other tests to identify which disorder is present. Other conditions that may be confused with seborrhoeic dermatitis based on appearance are listed below. • Atopic dermatitis (eczema) • Contact dermatitis • Psoriasis • Tinea capitis and tinea corporis • Candidiasis • Tinea versicolor • Pityriasis rosea • Impetigo • Drug reaction • Cutaneous T-Cell Lymphoma ==Management==

Medications A variety of different types of medications can reduce symptoms of seborrhoeic dermatitis. Calcineurin inhibitors were also effective in reducing the growth of Malassezia, offering two routes by which they may treat seborrhoeic dermatitis. Keratolytics Keratolytics help the skin via exfoliation of built-up skin flakes and thereby remove scale. They are applied topically to the affected area. Keratolytics include urea, salicylic acid, coal tar, lactic acid, pyrithione zinc and propylene glycol. Other treatments • Isotretinoin, a sebosuppressive agent, may be used to reduce sebaceous gland activity as a last resort in refractory disease. However, isotretinoin has potentially serious side effects, and few patients with seborrhoeic dermatitis are appropriate candidates for therapy. • Topical 0.75% and 1% Metronidazole Phototherapy Another option is natural and artificial UV radiation since it can inhibit the growth of Malassezia yeast. Some recommend photodynamic therapy using UV-A and UV-B laser or red and blue LED light to inhibit the growth of Malassezia fungus and reduce seborrhoeic inflammation. == Outcome ==

Seborrhoeic dermatitis is generally a chronic and recurring condition. Individuals may have the condition for several weeks to months, but it may also last years or their lifetime. There may be periods of relapse and worsening. ==Epidemiology==

Seborrhoeic dermatitis affects 1 to 5% of the general population. It is slightly more common in men, but affected women tend to have more severe symptoms. but often occurs during the first three months of life then again at puberty and peaks in incidence at around 40 years of age. == References ==