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.
In this article, 'Hair care' is taken to mean care of hair on the human head, but mention should be made of process and services which impact hair on other parts of the body. This includes men‘s and women’s facial, pubic, and other body hair, which may be dyed, trimmed, shaved, plucked, or otherwise removed with treatments such as waxing, sugaring, and threading. These services are offered in salons, barbers, and day spas, and products are available commercially for home use. Laser hair removal and electrolysis are also available, though these are provided (in the US) by licensed professionals in medical offices or speciality spas.

Hair cleaning and conditioning

Biological processes and hygiene

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. (Indeed, even well-to-do households can experience head lice. 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.

Hair cleaning

To combat this appearance of dirty hair and to remove actual dirt and other contaminants and external substances like sweat, the hair may be washed. Often hair is washed as part of a shower or bathing with a specialized soap called shampoo. Those with damaged or curly hair, or sensitive scalps, may benefit from cleansing with a light conditioner instead. However, this requires that only water-soluble products are applied to the hair and scalp.
Shampoo is helped by warm temperature water, which helps open the cuticle of the hair and release any oils or other substances beneath. Pure water has a pH of 7, and when shampoo has removed the slightly acidic sebum from the hair, the pH on the surface of the scalp is raised. Freshly shampooed hair can feel tangled or rough, and hair which is left to dry after a shampoo only can be excessively dry and coarse. To smooth the hair, conditioner is often used. Conditioners may employ ingredients of an acidic nature to balance the hair and scalp pH. Many modern conditioners also contain plant oils or synthetic ingredients such as plastics to coat the hair shaft and smooth it out. Acidic rinses or chemical conditioners can help with hair de-tangling and manageability, which helps prevent damage.
The sebaceous glands increase or reduce their secretions in order to maintain proper skin protection and pH. When the skin is regularly stripped of its natural sebum, the sebaceous glands respond with an overproduction. People observe that they “must” wash their hair, for example, once every other day, otherwise their hair becomes oily; however, their sebaceous glands have simply adapted to their hygienic cycle. Changes to the hygienic cycle result in changes to sebum secretion.
Modern shampoos and conditioners are not necessary to maintain clean and healthy hair, many cultures do not have these products at all. Different methods are available for those people who wish to return to this “natural” hair state, where healthy hair can be maintained with scalp massage, water-only washes, or using cleaning agents very rarely. Natural baseline sebum secretion varies by individual, and returning the scalp to this state takes time. This process may often include using cleaning agents, but is generally geared towards leaving the sebum on the scalp and hair for as long as possible to recondition the scalp to producing less sebum. In fact modern shampoos strip some nutrients from the hair while the shampoo cleans it. This is why it is recommended that you follow up by using some conditioner too which puts some of the much needed nutrients back into the hair. That is why hair dye comes with a bottle of heavy duty conditioner, because dye is very bad for your hair so they package in some heavy duty conditioner to help balance things and take away some of the negative effects of using their product.

Western cleaning products and methods

A more alkaline rated (meaning a high pH) shampoo is stronger and harsher to one's hair. This can mean that the hair will be left dry and brittle. Shampoos containing citric, lactic or phosphoric acid are most likely balanced. Oily hair might require a more acidic pH shampoo. Anti-dandruff shampoos have been implicated in irritation of the scalp, and an increase in the production of dandruff. Anti dandruff shampoos may be available over-the-counter or on prescription, based on the strength of the medicine. Dandruff, despite common belief, is more often related to too much, or an issue somehow with, sebum production and not dry scalp skin. Not all flakes are dandruff and only a qualified physician can determine not only that one indeed does have dandruff; but also, what type of dandruff one may have. If one is experiencing redness of the scalp skin, bumps on the scalp skin, and any weeping from sores and/or bleeding in addition to flakes, professional medical diagnosis should be sought.
Conditioner choice is greatly dependent upon hair type and hair status, such as colored, permed, dry, and the like. Commercial conditioners contain a variety of ingredients such as plant oils, provitamins, acidic compounds, plastics, stabilizers, thickeners, emulsifiers, and fragrances.
Conditioners may sometimes add weight to hair, creating an adverse effect in the shampooing/conditioning process. Some conditioners, especially those containing a silicone compound, may coat the hair and lead to build up on the hair, making it dull, and lead to harsher shampoo use; in a sense, an endless cycle of shampooing and conditioning. When used correctly, however, conditioners are helpful in temporarily coating the hair to increase shine and ease tangles.
Build up is when the hair has a sticky or gummy feel, the conditioner choice seems to work less well, or the hair may be more prone to tangling. Buildup occurs when the minerals from water and/or products are not rinsed away during shampooing. A clarifying shampoo may be required to remove it. Clarifying removes all things on the surface of the hair strands, essentially leaving the hair without moisture. Failure of conditioning as part of a clarifying hair wash process may lead to excessive drying of hair.
Viable natural ways to condition the hair include rinses with lemon juice, lime juice, vinegar or for brunettes, rosemary tea. The use of acid rinses may assist those who have itchy scalps, depending on the cause for the itchiness. Hair which is lacking sebum may also be softened using plant oils such as olive oil and coconut oil.

Washing

There are various ways to shampoo hair, and selection of a method is determined by one's hair type and available resources.
The most common method of hair washing is shampooing followed by conditioning. If there is a day or more between hair washings, then the first shampoo may only break up the surface tension of sebum, and a second shampoo application to the scalp hair may be necessary to thoroughly remove the sebum.
To help lift any scaly skin, detritus, and sebum from the scalp, especially for those who suffer from scalp skin ailments, very gently scratching the surface of the skin with a small fine toothed comb may help to loosen and lift grime and dead skin cells before washing the hair. This may help create a cleaner scalp during the hair washing process.
Microfiber towels that help absorb the water from hair faster than conventional towels are available on the market. These are particularly helpful for those with very thick hair that may otherwise take a while to dry, especially if air drying.