The most important and interesting attribute of phospholipids is their ability to form special molecular structures called liposomes. The molecular shape of a phospholipid consists of a water-loving head and two oil-loving tails.
When placing a large number of these molecules into a limited space they will arrange themselves spontaneously to match their heads together and also their tails.
The figure above shows the arrangement of a section of a living cell membrane which consists largely of phospholipids. As you can see, the phospholipid molecules have arranged themselves to form a membrane so that oil droplets cannot penetrate the cell membrane because they would be repelled by the wall of hydrophilic heads. In like manner, no water can penetrate the membrane because the lipophilic tails inside will not allow passage. The only access through the membrane is by special protein molecules that are programmed to let only certain chemicals pass in and out of the cell.
Plant phospholipids are all very similar in structure and composition. Under certain physical conditions they will spontaneously form microscopic spheres whose walls are very similar in construction to the actual cell membrane shown above.
The size of these spheres is very small, in the order of a nanometer. As illustrated, the spheres are hollow inside and enclose some of the liquid material in which they were formed (inclusion). Because of the small size of the phospholipid molecule and microspheres, they can pass through the epidermis and act as a carrier for the enclosed substances. It is postulated that when they reach the outside of a living cell membrane in the dermis they may become accepted as part of the membrane, being of the same composition. This process is as shown.
Thus, they are able to carry with them any enclosed substances into the dermis and to the individual cells.
The ability of phospholipids to act as the carrier mechanism for delivering active ingredients directly to the cell level has extensive implications for cosmetics. By themselves they are absolutely non-toxic and cause no skin irritations, not even around the eyes. Their danger lies in their ability to carry toxic or contaminated substances into the cells. The development of liposome technology offers the potential for many beneficial cosmetic products. However, the cosmetic developer has to deal very carefully with the selection of raw materials and the question of the biological fate of the preparation. The microspheres themselves are constantly undergoing changes due to thermal activity during preparation and storage. As a result, each ingredient of the preparation can end up inside the microspheres over time.
More than 80 percent of the cosmetic products on the market contain toxic substances that if used in liposome products will eventually become part of the inclusion inside liposomes that, in turn, will get inside your skin cells. Therefore, beware of products with liposomes that also contain substances causing adverse effects. As an example, preservatives fall into this hazardous category since they are all cellular toxins.
It has not been decided by the FDA whether liposome products with inclusions should be considered a medicine and put under the scrutiny of medical doctors with the advantage of documenting and tracking of potential long-term adverse effects. According to the Cosmetic Handbook, published by the Food and Drug Administration, “Products that are cosmetics but are also intended to treat or prevent disease, or affect the structure or functions of the human body, are considered also drugs and must comply with both the drug and cosmetic provisions of the law.“1 Some combinations of liposomes and active substances certainly qualify for this category.
1 U.S. Department of Health and Human Services, Cosmetic Handbook, U.S. Government Printing Office.