Humidity skin barrier function

Histamine receptors are related to skin barrier function.44 Three different types of histamine receptors, HI, H2, and H3 have been reported. First, topical application of histamine HI and H2 receptor antagonists accelerated the barrier repair. Histamine itself, H2 receptor agonist, and histamine releaser delayed the barrier repair. Histamine H3 receptor antagonist and agonist did not affect the barrier recovery rate. Topical application of the HI and H2 receptor antagonists prevented the epidermal hyperplasia induced by barrier disruption under low humidity. The mechanism of the relationship between the histamine receptors and the barrier repair process has not been elucidated yet. 

Dry, scaly skin is characterized by a decrease in the water retention capacity of the stratum corneum (SC),1 with water content diminished to less than 10%. Barrier function of the SC is usually declined, and transepidermal water loss (TEWL) is increased because of an abnormality on barrier homeostasis.2 People feel tightness of their skin, and the skin surface becomes rough, scaly, and sensitive. Hyperkeratosis, abnormal scaling, and epidermal hyperplasia are usually observed in the dry skin.2 Keratinization also shows abnormal features.2 These phenomena are commonly observed in atopic dermatitis and psoriasis.3 Dermatitis induced by environmental factors such as exposure to chemicals, low humidity, and UV radiation also shows these features. Thus, many researchers have been investigating the cause and treatment of dry skin, and there is currently great interest in adequate model systems for dry skin studies. In this chapter, I will describe several model systems of dry skin for clinical research of dermatitis associated with skin surface dryness and also mention recent studies to improve the dry skin. 

Seasonal changes affect the condition of normal skin and may trigger various cutaneous disorders.28,29 In common dermatitis, a decline in barrier function often parallels the increased severity of clinical symptomatology. All these conditions tend to worsen during the winter season when humidity is low.30,31 Abundant indirect evidence indicates that decreased humidity precipitates these disorders, whereas, in contrast, increased skin hydration appears to ameliorate these conditions. The mechanisms by which alterations in relative humidity might influence cutaneous function and induce cutaneous pathology are poorly understood. 

The main environmental occupational factors that interfere with barrier function and cause dry skin are (1) physical factors, e.g., temperature, relative humidity of the air and ultraviolet rays (UVRs) (2) mechanical factors, e.g., repeated skin rubbing and strain and (3) chemical factors, e.g., solvents, surfactants and water. 

Low humidity of the air is believed to cause dehydration of the horny layer and impairment of the epidermal barrier function (Agner and Serup 1989), i.e., increased irritability of the skin. Subclinical xerotic changes may occur within hours of exposure and are more pronounced in atopies (Eberlein-Konig et al. 1996). 

Interestingly, unexposed skin also displays an impaired epidermal barrier function (Agner and Serup 1989), which may indicate that even the wearing of protective (warm, wind-tight) gloves may not be able to completely abolish the effect of low humidity on the skin of the hands. As the hands may additionally be exposed to a variety of occupational irritants or to wet work, and as (sub-) clinical irritation is often known to be a multifactorial process (Malten 1981), this fairly inalterable environmental condition puts extra emphasis on the necessity of adequate skin protection, be it domestic or occupational. 

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