In vivo assessment of n-alkyl-sulfate-induced skin irritation by means of non-invasive methods

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Abstract

Background/aims:

Sodium lauryl sulfate (SLS) is the most frequently used model for studying in vivo irritation. It is also one of the most frequent surfactants in soap preparations and cosmetic emulsions. To investigate the irritant potential of sodium salts of n-alkyl sulfates with different carbon chain length (n=8, 12, 14), we applied these substances on the volar forearm of 10 healthy human volunteers aged 24 to 35 years.

Methods:

To allow the equal solubilization of the surfactants, we used a 0.2% solution (w/v). A colorimeter to assess erythema, an evaporimeter to assess transepidermal water loss (TEWL) and a corneometer to evaluate skin hydration were employed to estimate the effects of the chemicals on the skin. Evaluations were performed at baseline, 24, 48 and 72 h.

Results:

TEWL had increased at 24 h: SLS showed the highest increase, followed by octyl and tetradecyl sulfate. Skin hydration was reduced for the three substances, and a slight increase in redness was noticed. TEWL and hydration values at different times of assessment enabled the ranking of n-alkyl sulfates in the following order: lauryl sulfate, tetradecyl sulfate and octyl sulfate.

Conclusions:

We could not prove a direct correlation between barrier impairment, skin dehydration and surfactant-induced inflammation, as evaluated by color measurements. This discrepancy suggests that the irritation potential of n-alkyl sulfates at the dermal level differs from their action on skin barrier.

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