Science of Skin

Skin care concepts

SkinConcepts

Key concepts

The following are key terms used to describe the various functions of the ingredients in skin care products. They may prove a useful tool for understanding the A-Z of skin care ingredients. 

Antioxidants - Antioxidants are molecules which neutralise and stabilise reactive oxygen species (ROS) produced by the body. When present in large amounts, ROS can damage skin cells, thus antioxidants protect the cells by mopping up any excess. Additionally, antioxidants are able to reduce skin inflammation. Inflammation can decrease the collagen fibres which give skin its plumpness and flexibility. Some antioxidants also protect against damage to skin cells by UV radiation which can lead to skin aging and cancer formation.

Botanicals - Botanicals in skin care products are used for their antioxidant action; mopping up excess reactive oxygen species which can damage skin cells. Botanicals are derived from organic (natural) sources and form three broad categories based on their chemical structure: flavonoids, polyphenols and carotenoids.

Broad Spectrum - Broad spectrum refers to a sunscreen’s capacity to protect against various types of ultraviolet (UV) radiation. Traditionally sunscreens only offered protection against the B spectrum of UV radiation, in recent years it has been discovered that UVA (320-400 nm) radiation can also damage skin cells. Broad spectrum sunscreens reduce potential damage caused by both by UVA and UVB (290-320nm) wavelengths of light.

Buffering agents - Buffering agents minimise changes to a product upon the addition of acidic or basic components. The pH refers to how basic or acidic a substance is, with 7 being neutral, higher numbers being more basic and lower numbers being more acidic. The natural layer of sebum and sweat covering the skin is slightly acidic, with a pH of approximately 4 to 5.5. It functions to protect against weather, pollutants and disease. Thus, the pH of a skin care product must be close to the skin’s natural range to avoid altering this protective balance and damaging the skin.

Comedogenic - Comedogenic substances block the skin pores through which sebum, from sebaceous (oil-producing) glands beneath the skin, reaches the surface.

Cosmeceutical - Cosmeceuticals are substances which provide both a therapeutic and cosmetic effect.

Emollients - Emollients smooth the skin by filling gaps between the corneocytes (skin cells in the outermost layer of the epidermis) and adding volume to the medium between them. Usually oils and fats (lipids), emollients improve the touch and appearance of skin, increase flexibility and restore suppleness. They also lubricate the surface and fill in cracks and creases to even out its surface. A broad range of substances serve as emollients, each imparting a slightly different quality or feel. Many humectants also act as emollients.

Emulsifier
Figure 1. The function of an emulsifier

Emulsifiers - Emulsifiers allow two separate liquids to form a smooth cream or gel. Many creams and lotions are emulsions; a mixture of oils and water. Usually these two substances are immiscible (unblendable), as they tend to disperse and separate. An emulsifier is an ingredient which enables the two to blend well and stabilise.

Filters - Filters are the active ingredients in sunscreens, these can be divided into organic filters and inorganic filters. Organic filters have a chemical action of absorbing UV radiation. In contrast, inorganic filters' primary mechanism of protection is a physical one; they reflect and scatter UV radiation. Filters are often combined to cover a wider spectrum of UV radiation or so that the advantages of one are able to compensate for the drawbacks of another. Common filters include; avobenzone, the benzophenones, anthranilates, para-aminobezoic acid derivatives, salicylates, and cinnamates.

Humectant
Figure 2. The action of a humectant drawing water into the stratum corneum

Humectants - Humectants act by drawing available moisture from the dermis and epidermis out into the stratum corneum (exterior layer of skin). They also allow the skin to absorb moisture from the surrounding air when humidity is high (>80%). By hydrating the outer layer of skin, humectants make skin appear more plump and smooth. Water in this layer may still evaporate, so humectants are often combined with occlusives to prevent transepidermal water loss. Humectants also commonly act as emollients, encouraging soft, smooth skin.

Natural moisturising factor (NMF) - The natural moisturising factor, or NMF, is a mixture of molecules within the cells comprising the outermost layer of the skin (corneocytes). These molecules are hygroscopic, meaning that they attract and absorb water, and thus help hydrate the corneocytes. Half of the molecules making up the NMF are amino acids and the other half salts, such as lactates, urea and electrolytes.

Occlusive
Figure 3. The function of an occlusive

Occlusives - Occlusives function by creating a physical barrier covering the skin through which water cannot pass and hence be lost through the surface. They limit transepidermal water loss through evaporation, allowing the skin to retain moisture. Studies show that a stratum corneum (upper layer of the epidermis) with a water content of 20-35 percent functions normally. Dehydration causes fine lines on the skin; by maintaining higher water content, occlusives minimise such creases. Many occlusives also have emollient properties, evening out and softening the skin.

Sun Protection Factor (SPF) - The SPF describes the level of protection a sunscreen gives from ultraviolet (UV) B radiation (290-320 nm), the wavelength of light responsible for sunburn and known to cause skin cancer. The higher the SPF, the better the protection. An SPF of 30 or more is deemed ‘high’, blocking out 97% of UVB radiation over a specific period when a sunscreen is properly applied.

Sunscreens - Sunscreens are skin care products which protect the skin from damage by ultraviolet (UV) radiation; some also protect skin from visible light. Sunscreens contain active ingredients known as filters. Filters act by either absorbing visible light/UV radiation or reflecting and scattering it. The long-term effects and safety of most sunscreens for human use continue to be researched.

References

  • Draelos, Z.D, 2009, ‘Active Agents in Common Skin Care Products’, Plastic and Reconstructive Surgery, 125(2):719-724.
  • Kraft, J.N & Lynde, C.W, 2005, ‘Moisturizers: What They Are and a Practical Approach to Product Selection’, Skin Therapy Letter, 10(5):1-11.

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