Skin collagen: More than meets the eye.

Collagen is not like most proteins, which are essentially compact molecular clumps -- it is basically a fiber or, when fully mature, a mesh of fibers. Not surprisingly, collagen's composition is also unusual. It is particularly rich in four amino acids: lysine, proline, hydroxylysine and hydroxyproline. The most common patterns in the amino acid sequence of collagen are lysine-hydroxylysine-proline and lysine-hydroxylysine-hydroxyproline.

The types of collagen

Collagen is found in the majority of organs, not just the skin. It occurs in different forms known as types. Hence, it is not enough to have the right amount of collagen in the right place - it has to be the collagen of the right type.

• Type I Collagen - The most abundant collagen in the body. Found in tendons, bones, skin and other tissues. Particularly abundant in the scar tissue.
• Types II, IX, X, XI - Cartilage
• Type III - Common in fast growing tissue, particularly at the early stages (Phase 1) of wound repair. Much of it is replaced later by the type stronger and tougher type I collagen.
• Type IV - Basal lamina (filtration membrane of capillaries)
• Type V, VI - Generally found alongside type I
• Type VII - Epithelia (lining of GI tract, urinary tract, etc.)
• Type VIII - Lining of blood vessels
• Type XII - Found alongside and interacts with types I and III

The most abundant types of collagen in the skin are I and III; their fibrils form the mesh largely responsible for the skin's mechanical properties. Other types of collagen in the skin are V, VI, and XII. They are found in much smaller amounts and appear to have a supportive role, whose details remain unclear.

Types of collagen and the aging process.

Overall, the amount of collagen in the skin tends to decline with age. However, different types of collagen behave differently. In particular, a child's skin has a lot of collagen III, the type is common in fast growing tissues. The abundance of the type III collagen is partly responsible for the softness of the young skin. As the body growth slows down, the skin content of type III collagen declines, while that of type I increases. In fact, type I collagen continues to build up until about the age of 35, when the skin reaches the peak of its mechanical strength. After that, type I begins to decline as well. The dynamic of age-related changes in other collagen types remains unclear. However, we do know that by the age of 60, all types of collagen are significantly below their youthful levels.

Understanding collagen types is important for a number of reasons. First, different agents capable of stimulating collagen synthesis may affect different collagen types differently. That's one reason why some collagen boosters are more appropriate for the skin than others. Second, if you know the optimal skin collagen composition and could measure your own, you may have a better chance of selecting skin care that will work for you. Unfortunately, skin collagen composition analysis is still confined to advanced research facilities and the effect of most skin care treatments (with some notable exceptions, such as vitamin C) on specific collagen types remains unknown. But much research is going in that direction and its results may enter consumer market relatively soon.

Quantity vs quality

Having a lot of collagen in your skin is not enough. Even having the right mix of the collagen types is not enough. It is also important that collagen be undamaged and properly deposited. Collagen freshly deposited by young, healthy fibroblasts has a coherent and orderly structure. When collagen is damaged by UV rays, free radicals, impaired glucose metabolism, smoking or other factors, its structure becomes distorted, leading to poor skin texture, wrinkles and other imperfections. In this scenario, a common approach is to clear up the damaged collagen (e.g. via a peels, laser, activation of proteases or other means) and then stimulate the production of a more regular new collagen. Many skin care procedures and products address one or both steps of this approach.

Synthesis vs degradation

Most components of the skin, including collagen, undergo continuous turnover. New collagen is continually produced and recycled throughout life. At a younger age the synthesis of collagen predominates, whereas after about age of 40, the degradation of collagen picks up speed. Therefore, to keep your skin's collagen in balance, after certain age you may benefit from steps to boost collagen synthesis and reduce its degradation.

Considering that collagen type I and III seem to predominate in the skin, the agents and treatments shown to stimulate the synthesis of these types are particularly promising. One good example of such an agent is topical Vitamin C, whose capacity to stimulate both type I and III collagen has been shown in a number of studies. (We discuss the use of vitamin C and other collagen boosters in the Anti-aging Treatments section and Skin Rejuvenation Infopack.)

Just like the synthesis, collagen degradation is an ongoing, natural process. You may ask: why would the skin want to destroy its key structural proteins? Isn't it like cutting the legs of your own chair? Well, not quite. There are situations when removing collagen makes sense, e.g. when collagen it excessively damaged or when there is an infection and a passageway needs to be cleared for the immune cells. But as we age, collagen degradation tends to spin out of control and contribute to weakening and wrinkling of the skin. On top of that, a number of external factors increase it even further: UV rays, smoking, chlorinated water, free radicals, inflammation, irritation and others. Minimizing all of the above is always a good idea but may not be enough to keep collagen degradation under control. A more advanced approach is to inhibit the enzymes called matrix metalloproteinases (MMP-s). These enzymes (particularly the one called collagenase) chopping up collagen into small pieces which then get recycled.

Considering that older skin does not respond to collagen synthesis boosters particularly well, inhibiting the degradation of collagen by MMP-s -- used alone or in conjunction with stimulating the synthesis -- may prove to be a better approach. Much research is currently being done to find effective topical MMP inhibitors. Unfortunately, despite claims by some manufacturers, none of the topical agents currently on the market has been proven to directly inhibit MMP-s. However, such agents are likely to appear in the near future. In the meantime, it is useful to know that some common skin care ingredients appear to inhibit MMP-s indirectly, e.g. by inhibiting certain pathways of inflammation or suppressing the synthesis of MMP-s. Such agents include lipoic acid, retinoids and others (see our Anti-Aging Treatments section).