Sebaceous glands
In addition to its role as a protective barrier, sebum also has antibacterial properties, conferred by oleic and palmitoleic acids, as well as antioxidants, conferred inter alia by vitamin E.
The level of secretion of sebum differs from one individual to another and will be at the origin of different types of skin texture: Dry skin or brittle hair will be the consequence of a low secretion of sebum, while a skin or greasy hair will be the consequence of a greater sebum secretion known as hyper-seborrhea. This hyper-secretion of sebum can also be responsible for skin disorders such as acne.
Sweat glands:
The sweat glands, which contribute entirely to the secretion of sweat, the evaporation of it leads to the cooling of the skin and plays a large role in the regulation of body temperature. In addition to their role in regulating body temperature, they also eliminate some metabolic waste.
This means that the sweat they excrete is a hypotonic fluid derived from the filtration of blood plasma, composed of water and electrolytes, allowing thermoregulation through transpiration.
What about hairs:
Hair and hair in general are vestiges of evolution. Because the Australopithecus (our distant prehistoric parents of 3 million years ago) like most mammals have a fur whose main function is to help maintain a constant body heat in very cold weather.
In case of excessive cold, it is the brain that is affected first: hypothermia can have very serious consequences. The blood vessels irrigating the brain regulate its temperature. If these cool too close to the outside air, the brain will suffer because security systems such as narrowing vessels are limited.