In the 1950s, Blank demonstrated that low moisture content of the skin is a prime factor in dry skin conditions.1 It is now known that the symptoms of dry skin can be treated by increasing the hydration state of the stratum corneum with occlusive or humectant ingredients; smoothing the rough surface with an emollient; restoring the integrity of the skin barrier; increasing natural moisturizing factor (NMF) or the activity of aquaporin; and controlling the calcium gradient. Choosing the correct cleanser is also crucial in the treatment of dry skin (see Chapter 6, Overview of Cleansing Agents).
Various types of moisturizers are combined to form the best strategy for treating the underlying issues leading to dry skin. Several factors should be taken into account when choosing the type of moisturizing ingredients. The first is the Baumann Skin Type (BST) (see Chapter 1, The Importance of Skin Type: The Baumann Skin Type System). The level of dryness determined by the Baumann Skin Typing System (BSTS), designated by D1 D2 D3, gives information about the severity of skin dryness. A higher D score such as D3 indicates that more than one defect is contributing to skin dryness and that multiple strategies should be chosen. If the BST also includes type 4 sensitive (S4) skin, then there is evidence that the skin barrier is severely impaired and the barrier repair strategy should take top priority. If the Baumann Skin Type Indicator (BSTI) questionnaire that determines BST detects signs of increased sebum secretion, then an occlusive moisturizer would be unnecessary because sebum is a great occlusive moisturizer. Individuals who have dry skin with increased sebum secretion likely have defects such as impaired aquaporin function, decreased NMF, altered calcium channels, or they may be using barrier-disturbing cleansers that are leading to the dry skin. Noting the humidity level of the environment prior to choosing a moisturizer is important because humectant ingredients work better in a humid environment. Knowing habits such as increased sun exposure (which lowers NMF) and prolonged immersion in water (which disturbs the skin barrier) can also give clues about the causes of dry skin.
The ingredients in this chapter are divided into subsections according to their mechanism of action. Some ingredients have more than one mechanism of action. In that case, they will be discussed in the subsection that displays the unique characteristics of that ingredient and distinguishes it from others. For example, glycerin is a well-known and very effective humectant, but it has the unique property of being able to pass through the aquaporin channels so it will be discussed in the aquaporin subsection. The mechanisms will be briefly explained at the beginning of each subsection. For more detailed information on the causes of dry skin, see Cosmetic Dermatology: Principles and Practice, 2nd edition, McGraw-Hill (2009).
Emollients are substances added to cosmetics to ...