The waxy and oily substance in people’s hair called sebum
Sebum is an oily and waxy substance produced by glands situated around hair follicles just below the scalp and in the rest of the body, only palms and soles lacking sebaceous glands. It’s produced throughout our lives, starting as fetuses between the 13th and the 16th week, when it appears more like a waxy coating of the skin to protect from the amniotic fluid.
Its composition and quantity changes various times over the years, with peaks of production during puberty and pregnancy, with definite lows later in life, which explains dry hair and skin in the elderly. The amount of sebum produced also changes from individual to individual.
In fact, sebum has multiple functions, including keeping the skin and hair from drying excessively by locking in the moisture, but also protecting it from excessive humidity from outside by waterproofing it. It also protects from extreme temperatures, acting as insulation from the cold and controlling the loss of sweat in the heat, and from bacteria and fungi related infections, viruses and external contaminants acting as a shield between the threats and the skin and hair. Just like for skin, sebum is also a lubricant for hair thanks to the oily and waxy composition.
When secreted in excess and not removed appropriately, it can clog the follicles and cause a bacterium to reproduce at such a high rate that it clogs follicles and eventually causes acne.
Sebum reaches the skin through the follicles by adhering to hair which brings it to the surface and then spreads over the skin and the hair.
Per se, sebum is odorless, however, when exposed and broken down by bacteria, it generates an unpleasant smell.
Over time it accumulates regardless of the intensity of secretion, so to avoid the smell, the bacteria, the oily look and feel, and all the downsides of the build up, it’s necessary to wash it off, and since it’s a fatty substance, a detergent is required. Typically, it’s done by washing with shampoo, or shampooing, which is a specific type of detergent formulated to clean hair.
Different individuals require different frequency of washing, in most cases ranging from a minimum of 3-4 times a week to once every couple of weeks. Excessive washing will dry out skin and hair, while too little will allow an unsanitary build up and growth.
Especially build up opens the doors to parasites, bacteria, fungi, viruses and retention of contaminants and accumulation of byproducts.
Washing too often reduces the amount of protection, good bacteria, dries, weakens and cracks skin and hair and, apparently, increases the rate of production of sebum to naturally make up for the loss of that same substance that shampooing is trying to get rid of.
Normal levels of sebum on the hair and skin are, therefore, healthy, while an excessive accumulation or too little on skin and hair, are unhealthy and efforts should be made to find the right compromise when deciding how often to wash with soap or shampoo.