Anti-irritants II: Efficacy against cumulative irritation.

So-called anti-irritants (AI) are widely used in cosmetic formulations, with the aim of reducing irritation from substances in the formulation. It may also be claimed that they are 'soothing' and 'healing' ingredients. However, the proof for these claims is circumstantial. The dose-response effect of 4 alleged AI (nifedipine, (-)-alpha-bisabolol, canola oil and glycerol) was studied on experimentally induced acute irritation in healthy volunteers, and only glycerol showed dose-related response and effects potentially better than no treatment. The acute irritation model only allowed a small window of opportunity in which to demonstrate efficacy. Therefore, the effect of AI was studied in a cumulative irritation model by inducing irritant dermatitis with 10 min daily exposures for 5+4 days (no irritation on weekend) to 1% sodium lauryl sulfate on the right and 20% nonanoic acid on the left volar forearm. AI ointments were applied twice daily. Clinical scoring was performed daily, evaporimetry (Trans Epidermal Water Loss), hydration and colourimetry were measured at baseline (D0), in the middle and at the end of treatment. The glycerol ointment was the only treatment statistically better than both 'no treatment' and vehicle.

Anti-irritants I: Dose-response in acute irritation.

The term 'anti-irritant' (AI) was coined in 1965 by Goldemberg to describe a diverse group of topical product ingredients, which were able to reduce the irritation potential of other more irritating ingredients in the same product. 'AIs' are being added to cosmetic formulations in order, allegedly, to benefit tolerability of the products and allow claims such as 'soothing' and 'healing' ingredients. Limited documentation in favour of the efficacy of AIs is published. We studied the dose-related effect of 4 alleged AIs (nifedipine, (-)-alpha-bisabolol, canola oil and glycerol) on experimentally induced acute irritation in healthy volunteers. Each AI was used in 3 concentrations. Acute irritation was induced by occlusive tests with 1% sodium lauryl sulfate and 20% nonanoic acid in N-propanol. The irritant reactions were treated twice daily with AI-containing formulations from the time of removal of the patches. Evaluation of skin irritation and efficacy of treatments were performed daily for 4 days using clinical scoring, evaporimetry (transepidermal water loss), hydration measurement and colourimetry. Only glycerol showed dose-response and effects potentially better than no treatment. There was no significant effect and no difference between the three other AIs.

The potential of the essential fatty acid-deficient hairless rat as a psoriasis screening model for topical anti-proliferative drugs.

The objective of this study was to establish essential fatty acid deficiency (EFAD) in hairless rats and investigate the potential of this model as a psoriasis screening model by testing the effects of calcipotriol and dithranol on differentiation and proliferation in the epidermis. Hairless rats were fed with a fat-free diet lacking linoleic acid. The EFAD condition was established within 8 weeks. In order to ensure that this condition had been established, several parameters were measured and observed, i.e. animal weight, water consumption, transepidermal water loss, clinical skin symptoms, histology of the epidermis and fatty acid analysis of serum and skin. Immediately after the EFAD condition had been established, the animals were treated with dithranol ointment or different concentrations of calcipotriol solution. A reduction in epidermal thickness of 15-20% was seen after the treatment with calcipotriol. Dithranol and its coal tar-containing vehicle also showed a reductive effect on epidermal thickness. EFAD hairless rats possess various histological changes resembling psoriasis. These histological changes normalise during treatment with anti-psoriatic drugs as calcipotriol, dithranol and coal tar. The results of the present study indicate that the EFAD rat may be a useful model for studies of anti-psoriatic drugs affecting cell proliferation.