We all know that it is extremely difficult or practically impossible to recover the hair lost years ago. It seems that in all the human history there has not been any case in which the hair of a typical baldness has been recovered, just in a few particular cases it has been observed the outcome of a few hairs but without any aesthetical value.

Common baldness is usually a slow process, but it is inexorable, and as the time goes by it gets more difficult to pull out. Then, is such a radical process caused just by a detention in the sebum flow? Of course not, many other processes take part in the hair loss, the detention of sebum is the initial and triggering factor of the complex process of common baldness. It is the most important factor at the first stages of baldness, therefore it must really be taken into account if we wish to avoid and prevent baldness, in order to be able to invert the process at its initial phases. As time passes there is a degeneration and alteration of other processes which make the process much more difficult to be inverted, and turn it practically irreversible in the last stages.

Each pilosebaceous follicle contains the hair itself, made up by the dermal papilla, the hair shaft and several sheaths that cover the root area. There is a sebaceous gland joined to every hair which provides the sebum, essential to have a healthy hair. There is also an arrector pili muscle able to make the hair stand erect. There is a blood vascular system suitable for hair and an area next to the sebaceous gland duct, called bulge area, where the stem cells in charge of the cellular renovation of the dermal papilla, the sebaceous gland and the epidermis itself are located. There is also a neuronal net which connects with the hair at the bulge area (near the sebaceous gland) and later surrounds the base of hair.

Human sebum is mainly made up by a heterogeneous mixture of triglycerides, fatty acids, wax esters and scualene and in a smaller proportion of cholesterol and cholesterol esters along with vitamin E (alpha and gamma tocopherol). Lipids are synthesized at a constant rhythm in the sebaceous gland and are secreted to the outside after 8 days. At skin temperature, sebum is composed of a liquid phase which dissolves a solid phase, and when a bigger percentage of saturated species appears at its composition , the percentage of solids increases and the viscosity rises.

Observing the process in more detail it can be said that the first serious problem to happen is the detention of sebum flow towards the inner part of the hair follicle. There are some observations which support such thesis, as the fact that inside the hair there are lipids which are similar to the ones found in sebum. Such lipids make a kind of cement that joins the hair fibres, and it seems that they are in a bigger quantity at the hair marrow (the most inner part of hair). The only way to get to the hair is through the lower part of the root of hair. And where does the detention of this flow towards the inside come from? It comes from an alteration of the flow towards the outside. This is analogous to economic theory: when the demand of a product increases or decreases disproportionately in one sense, then the risk of destabilization for the rest of the consumption nets appears, if such disorder continues for a long time, the expenses are increased. In this case if the sebum flow towards the outside is stopped, with the time the sebum flow to the inside will be altered.

This observation is what makes this theory really innovating, nobody till the moment has showed the way of sebum to the inside of the hair follicle. Nobody has indicated sebum as a kind of nutrient of hair.

Another detail is that hair itself, due to its lipidic composition, is useful as a mean of transport of several biologic signs such as the hormones. It is also very likely that sebum takes part in the transport of stem cells produced at the bulge area, just below the duct where the sebaceous gland pours the sebum to the hair follicle, and it addresses to the lowest part of the hair root.

This way is not easy, as it is narrow and it passes through external layers and shafts that cannot be trespassed. Besides, with the detention of sebum several alterations happen:

• There is a physical alteration, as its viscosity increases.
  
  
• There is a chemical alteration due to the oxidation processes of the sebum components.
  
  
• There is also a biologic change in its functions such as markers, hormones, as several components appear and/or disappear. The apparition of new components can create an inflammatory reaction, therefore the process gets worse, as it stops even more the flow of fat by expanding the tissues and decreasing the space where the sebum and its associate components should go by. Some microorganisms grow in sebum and are fed from it, and they are susceptible of creating rejection reactions due to the immune system, which makes the process get worse due to rejection reactions. Another of the most studied points is the hormonal variation, which increases the "harmful" DHT (Dihydrotestosterone), an hormone that gets accumulated.

This theory can explain the miniaturization process which appears in the process of alopecia, before its definite loss, and it is probably due to the fact that there is not a replacement of the stem cells to be able to create healthy dermal papillas which can support healthy hairs. One of the last processes, which makes the way back almost impossible is the destruction of the nervous system joined to hair due to the isoprostanes and other poisons for neurones, and especially at those neurones that don't have the protective shaft of myelin, being then more susceptible to suffering an external attack.

This theory could make reference to the reviled theory of the blocked follicles, but in this one they talk about a blockage towards the inside.