Skin hyper-reactivity

Another factor to consider is that patients with endogenous skin disease are frequently more susceptible to cosmetic reactions. One reason is that patients with preexisting skin disease may have skin barrier dysfunction, with consequent increased permeability. Skin hyper-reactivity in atopic patients, particularly, has been gathering interest in recent years. Epidemiologic associations between atopic dermatitis and irritant dermatitis are now supported by skin bioengineering data.25... 

Barrier Function and Skin Hyper-Reactivity in Atopic Eczema... 

Vitamin D3 has been reported to cause hyper-reactivity of skin with pseudoxanthoma elasticum (39). 

From a practical point of view, post-irritative hypo-reactivity probably represents another aspect of skin adaptation to environmental influences. Whereas post-irritant hyper-reactivity would explain the greater irritability of eczematous skin during patch testing, a hypo-reactive state may cause false negative patch-test results for as long as 9 weeks after an irritant reaction. 

It may be argued that the patch tests are positive because the skin is in a state of hyper-reactivity termed excited-skin syndrome or angry back (Bruynzeel and Maibach 1995). This may lead to strong positive reactions to patch tests of minor irritants or subclinical or weak allergens. Authors who report compound allergies, such as Cox et al. (1989) or Kellett et al. (1986), have eliminated this as far as possible by repeating the patch tests 2 months later and obtaining another positive result. 

Measurement of differences in skin reactivity or sensitivity among individuals plays an important role in the workplace, as well as in the manufacture of safe topical therapeutics and cosmetics. Outlined in the following sections are objective and subjective methods of quantifying the reactivity of human skin to chemicals, which are potential irritants.6 The experimental basis of such testing is to quantify the differences among individuals to chemicals that produce characteristic responses using a standard reproducible procedure. Individuals classified as hyper-reactors (sensitive skin) and hyporeactors can then be identified. 

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