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Chronic skin complaints such as psoriasis or eczema (formally known as atopic dermatitis) may occur due to genetic, environmental or lifestyle influences, or a combination of the three. Psoriasis may also afflict individuals taking certain prescription medications (including beta blockers, NSAIDS and lithium), or those with severely weakened immune systems—such as HIV sufferers. Prevalence of psoriasis varies widely between countries, and is estimated at around 2-4% in Western countries.
Lifestyle influences on occurrence and severity of common skin conditions include obesity, smoking, stress, general ill-health, poor diet, and alcohol consumption. Environmental causes include changes in season or climate, particularly those involving dramatic changes in humidity. For eczema, it is postulated that overly sterile human environments may contribute to development of allergies in children; as well as this, it is suggested that dust mite allergy is strongly associated with the condition. Eczema is estimated to affect around 10% of all humans, to varying degrees of severity; in some areas, lifetime prevalence is thought to be as high a one third of the population, and appears to be rising over time.
There are several forms of dermatitis, with the two most common forms being atopic or chronic dermatitis (eczema) and contact or acute dermatitis (which is caused by direct contact with an allergen or irritant, and is often mistaken for eczema). The symptoms generally range from red skin and bumpy rashes to severe blistering and lesions in severe cases. Blisters and lesions may weep or ooze and may ultimately lead to unsightly scarring.
Dry, itchy skin is the most common symptom; areas most commonly affected include the cubital and popliteal fossa (the inner fold of the elbow and knee, respectively), the wrists, hands and face. Eczema can be extremely debilitating, but is not fatal; however, resultant infections gaining a foothold through broken skin have occasionally been known to cause fatalities. Infection by staphylococcal or streptococcal bacteria is very common in eczema; rarely, this can lead to widespread infection and septicaemia. As well as this, the herpes simplex virus can infect eczema-damaged skin and cause an extreme condition known as eczema herpeticum, which can in turn lead to systemic bacterial ‘superinfection’ and even death.
Psoriasis also comes in various forms. The most common form is known as psoriasis vulgaris or plaque psoriasis. The ‘plaques’ this terminology refers to are raised, inflamed (often roughly circular) patches of skin covered with a silvery, scaly, plaque-like substance. These plaques usually appear on the elbows, knees, scalp, and back. Psoriasis vulgaris affects up to 90% of psoriasis sufferers; other forms include pustular psoriasis, which causes raised, pus-filled bumps or pustules accompanied by severe itching and tenderness. Pustules usually appear on the hands and feet, or randomly across the body.
A rare, potentially-fatal form of the condition is known as erythrodermic psoriasis; this debilitating disease can lead to inflammation and exfoliation of the majority of the sufferer’s skin. The severity of the inflammation and skin loss can be such that normal temperature regulation and barrier function control is irreparably disrupted and death can result.
Eczema sufferers have been found to exhibit variations in the FLG gene that encodes expression of a protein known as filaggrin, which is crucial to regulation of the stratum corneum, the outermost layer of the epidermis. Filaggrin binds to free strands of keratin and causes it to form a matrix within the keratinocyte cells of the epidermis. This tough, impermeable matrix is the foundation of the waterproof ‘barrier’ that makes up the outer layer of human skin; it keeps the skin hydrated both by preventing evaporation and by absorbing water. Variations in the FLG gene have also been implicated in another debilitating skin condition, ichthyosis vulgaris, which causes the skin to take on a scaly appearance due to over-production of keratinocytes.
Psoriasis, which also involves over-production of keratinocytes, has a strong genetic association; around one-third of sufferers report family history of the condition. It is thought that several genes interact to determine occurrence of psoriasis in ways that are not fully understood; around thirty-six different loci that correspond to psoriasis susceptibility have been found on the chromosomes. The genes found within these loci are involved in inflammatory response, and several have been implicated in other autoimmune diseases as well as psoriasis.
Both eczema and psoriasis involve an atypical immune response. Psoriasis is considered to be autoimmune in nature, as it does not occur due to any external allergen but due to a malfunction of the immune system that causes it to attack formerly healthy tissue. Eczema is a generalised response to the presence of external allergens, and is not an autoimmune disease—although it is often present in individuals suffering from other autoimmune diseases, and certain other forms of dermatitis have an autoimmune component.
Specifically, eczema and psoriasis are conditions that are caused by atypical inflammatory response. The inflammatory response is a fundamental part of the immune system: upon initial exposure to a pathogen (or perceived pathogen in the case of an autoimmune disease such as psoriasis), increased levels of blood plasma and white blood cells (particularly granulocytes) are then brought via the bloodstream to the affected tissues. These fluids then accumulate, causing the characteristic swelling; the increase in blood flow in the affected area causes reddening and the sensation of heat, and itching and pain occur due to release of compounds that stimulate the nerve endings.
Application of several different oils and emollients, such as petroleum jelly, beeswax, almond oil, olive oil, and various synthetic preparations, have been shown to reduce symptoms of psoriasis and dermatitis. As these conditions are characterised by overly dry skin, products which can moisturise the skin while avoiding further irritation are fundamental to their treatment. In eczema and psoriasis, dry skin occurs due to excessive transepidermal water loss, as persistent inflammation compromises the skin’s ability to act as a barrier and regulate diffusion and evaporation.