Why do you have sebum glands?

Glands that produce sebum, known as «sebaceous glands», are attached to each hair follicle shaft.
The number of glands can vary, but typically, one to four sebaceous glands are associated with each hair.
Hair follicles are found almost everywhere on the human body, except for: the palms of the hands, soles of the feet, lips, eyelids, penis, labia minora and most of the nipples.
The face and scalp have the highest concentrations, with up to 900 glands per square centimeter.

Sebum is an oily, waxy substance that is unique to mammals.
It's a natural lubricant.
Sebum prevents moisture loss by creating a waterproof barrier, preventing excess water from evaporating from the skin and keeping it hydrated.
Sebum keeps the hair shiny.

There is no passage to expel the sebum from the glands, except for the hair shaft itself.
Sebum is only ejected when the hair is forcibly bent.
If not, the sebaceous glands keep on producing; so they enlarge.
The skin of the whole body dries out.
For example, when sebum accumulates on the scalp, it mixes with other substances like sweat, dead skin cells, and hair products.
This buildup hardens and forms a crusty or scaly appearance on the scalp.
If left untreated, the buildup of sebum on the scalp can lead to dandruff, acne, local skin infection, and even hair loss.
Blocked sebaceous glands create pimples and blackheads plugs, and can lead to more severe skin problems.

Here's how it works.
Its a mechanical system.
Sebum is released when your nail inclines the hair shafts while raking the skin.
• As your fingertip and nail pass over your skin, they bend the base of the hair they encounter.
• This creates a mechanical pressure on the sebaceous glands to release some of the sebum.

Humans are primates.
Only primates have flat nails that can scrape the skin without hurting it.
All primate species groom their skin, every day, for extended periods; except humans.
There is no doubt that our ancestors were grooming in the past, and that we've stopped doing it at some point in our evolution.

Grooming is a natural behavior for primates that goes back about fifty million years.
Today's humans have concluded that grooming is useless; and their exploding sebum glands are only one of the many health problems that this decision has provoked.

So, what is the purpose of sebaceous glands?
Is it:
1• To oil the skin to hydrate it?
or
2• To oil the skin so it can be groomed?
The first answer makes no sense, because the sebum stays stuck inside the glands if the skin isn't groomed.
Grooming has several health benefits other than just releasing the sebum, including:
• Relieving pain,
• Raking off dead skin cells,
• Restoring nervous blockages,
• Increasing blood flow,
• Rejuvenating the skin,
• Preventing ugliness,
• ...

There are about six times more sebaceous glands on your head, where you are more folded, and where more grooming is needed.
Hair varies in size all over your body.
To equalize their lubricating effect, sebum glands are;
•Big on smaller hair (neck) and
•Small on bigger hair (beard).
On a human fetus, these same sebum glands secrete the white substance called Vernix caseosa; another waxy and oily compound that facilitates the passage of the fetus at birth.

Human grooming lets you use your nails to treat all kinds of skin and health related problems.
The following video will get you started:

We all have experienced sebum eruptions that exceed in quantity what we would expect from a few glands.
My grooming experience shows that the most problematic sebum build-ups are not in the glands themselves, but are the result of having several glands expelling their content inside a skin fold or a fold crossing, where the sebum accumulates.

The output from several glands is stored inside cutaneous folds, but mainly at their crossings.
However, since dermatologists don't recognize cutaneous folds (they think they are lines), this phenomenon is not understood.
Bad advice follows.