Everyone's skin is covered by a lipid mantle - a layer of fat produced by the sebaceous glands. Its function is to protect against sun, frost, wind, bacteria, viruses and fungi, as well as against water loss. There are also other fats in the skin that are well known to morphology: cholesterol and triglycerides. Their excess is undesirable in the blood because of the risk of atherosclerosis. For the skin, however, they are extremely important: they soften and moisturise, and help other nutrients to penetrate deep into the skin.