*2.2.3 Nicotinamide*

Nicotinamide, which easily penetrates the skin, is fast becoming a ubiquitous topical skincare ingredient in a range of moisturiser formulations. A number of clinical trials [79–81] show that the concentration of topical nicotinamide products can go up to 10%, but desired effects can be achieved with concentrations as low as 2–5% [79]. Nicotinamide provides a long list of skin care benefits with its use, including its ability to: (1) support the skin barrier structure and function by facilitating the formation of ceramides and keratin [74, 75]; (2) improve the skin's tone and texture [82]; and (3) boost the effectiveness of moisturisers in general [75]. For example, when formulated in a combination with glycerin, a nicotinamide-containing moisturiser can very effectively improve the integrity of the SC and thus reduce skin dryness over time [75, 83]. In addition, nicotinamide has also been shown to have anti-inflammatory and antioxidant properties, the latter of which may help to reduce the harmful effects of UV radiation, photoageing and oxidative stress [84]. The appropriate concentration of topical nicotinamide for each individual may depend on their skin type and condition, keeping in mind that in some instances, high levels of nicotinamide can cause an allergic reaction for people susceptible to skin allergies [85].
