An emerging aspect of effective use of skin-applied nutrition is absorption (permeation of epidermal and dermal barrier by the compound) and ultimately bioavailability of the compound to the target tissues and/or receptors
Cosmeceuticals or natural cosmetic ingredients i.e. vitamins, minerals and botanicals, some discussed above, may have different rates of absorption through the skin and bioavailability, depending on their chemical and biochemical forms
In discussing mechanisms of nutrient absorption and bioavailability, a key distinction should be stressed between these two concepts
The term bioavailability should not be used interchangeably as a definition of absorption. Therefore, besides the tissue level of a supplemented ingredient, e.g. dermal levels of genistein, the functional outcome of the supplementation should also be measured, e.g. impact of topical genistein on skin thickness in postmenopausal women
The former would measure the absorption rate of genistein and the latter would measure its true bioavailability
The consensus is that both events, the measurable absorption rate and target issue/receptor bioavailability of a nutrient, ultimately contribute to the efficacy of supplemented nutrient
Regulation and enhancement of nutrient or drug delivery to targeted skin cells (bioavailability) has great importance in skincare and skin health
An emerging new topical bioavailability enhancer is Tetrahydropiperine (THP), a derivative of pungent alkaloid piperine from the fruits of black pepper (Piper nigrum, fam. Piperaceae) and long pepper (Piper longum, fam. Piperaceae)
The parent compound piperine has been successfully evaluated orally for its potential to enhance the gastrointestinal absorption of drugs and nutrients in animals and humans
Compounds successfully studied include drugs such as vasicine, pyrazinamide, rifampicin, isoniazid, propranolol, theophylline and phenytoin, and nutrients such as fat-soluble beta carotene, water-soluble vitamin B6, vitamin C, coenzyme Q10 and the mineral selenium in form of L-selenomethionine
