Hair care is an overall term for parts of hygiene and cosmetology involving the hair on the human head.
Hair care will differ according to one's hair type and according to various processes that can be applied to hair.
All hair is not the same; indeed, hair is a manifestation of human diversity.
Care of the hair and care of the scalp skin may appear separate, but are actually intertwined because hair grows from beneath the skin.
The living parts of hair (hair follicle, hair root, root sheath, and sebaceous gland) are beneath the skin, while the actual hair shaft which emerges (the cuticle which covers the cortex and medulla) has no living processes.
Damage or changes made to the visible hair shaft cannot be repaired by a biological process, though much can be done to manage hair and ensure that the cuticle remains intact.
Scalp skin, just like any other skin on the body, must be kept healthy to ensure a healthy body and healthy hair production.
If the scalp is not cleaned regularly, by the removal of dead skin cells, toxins released through the skin or external hazards (such as bacteria, viruses, and chemicals) may create a breeding ground for infection.
However, not all scalp disorders are a result of bacterial infections. Some arise inexplicably, and often only the symptoms can be treated for management of the condition (example: dandruff).
There are also bacteria that can affect the hair itself. Head lice is probably the most common hair and scalp ailment worldwide.
Head lice can be removed with great attention to detail, and studies show it is not necessarily associated with poor hygiene.
More recent studies reveal that head lice actually thrive in clean hair.
In this way, hair washing as a term may be a bit misleading, as what is necessary in healthy hair production and maintenance is often simply cleaning the surface of the scalp skin, the way the skin all over the body requires cleaning for good hygiene.
The sebaceous glands in human skin produce sebum, which is composed primarily of fatty acids.
Sebum acts to protect hair and skin, and can inhibit the growth of microorganisms on the skin.
Sebum contributes to the skin's slightly acidic natural pH somewhere between 5 and 6.8 on the pH spectrum.
This oily substance gives hair moisture and shine as it travels naturally down the hair shaft, and serves as a protective substance preventing the hair from drying out or absorbing excessive amounts of external substances.
Sebum is also distributed down the hair shaft 'mechanically' by brushing and combing.
When sebum is present in excess, the roots of the hair can appear oily, greasy, generally darker than normal, and the hair may stick together.