Traditional Indian hair care practices

The head massage, performed with warmed oil, usually weekly, often by another person. It is among the most widespread hair practices on the subcontinent and it persists because it works well enough and feels good.

The plausible mechanism is straightforward. Oil lubricates the shaft, so combing and handling cause less friction and less cuticle wear. Massage is comfortable and encourages regular attention to the scalp. Applied before washing, oil reduces how much the hair swells and how much protein is lost during the wash.

That is a modest and defensible account, and it is enough to justify the practice without extending into claims about growth rates.

The detail that oiling comes before washing rather than after is the part most often lost when the practice travels. It matters. The oil is there to reduce the damage the wash itself causes, and then most of it is removed.

This is also why the traditional practice does not leave people walking around with oily hair. The oil is a pre-treatment, not a styling product.

Before commercial shampoo, hair was commonly washed with reetha, soapnut, and shikakai, the pods of Acacia concinna. Both contain saponins, naturally occurring compounds that foam and have surfactant properties.

They clean, more gently than a strong modern shampoo, and they are mildly acidic, which suits hair better than the alkaline soaps that historically damaged it. They also lather far less, which people used to modern shampoo often read as not working.

Practical caution: reetha stings badly in the eyes. Traditional preparation involves tilting the head back for good reason.

• Hibiscus leaves and flowers produce a mucilaginous slip when crushed, which makes hair easier to detangle. Used as a paste or infused into oil.
• Fenugreek seeds, soaked and ground, also give a mucilage with a conditioning slip. Distinctive smell that not everyone tolerates.
• Bhringraj, Eclipta alba, appears in a great many traditional hair oils and is one of the most commonly cited herbs for hair in Ayurvedic texts. Evidence in the modern sense is limited.

Pure henna, Lawsonia inermis, coats hair and deposits a reddish colour that binds to keratin. It is a genuine colourant and it also has a mild strengthening effect from that coating.

Two serious cautions. First, henna is permanent in the sense that it cannot be stripped easily, and it interacts unpredictably with subsequent chemical colouring or bleaching, so tell your colourist. Second, black henna is not henna. It typically contains PPD, a dye that causes severe allergic reactions in some people and is not safe for skin application at those concentrations. Avoid it.

Pure henna is also drying for many people, which is why traditional preparations mix it with oil, yoghurt or egg.

Pre-wash oiling and a slow scalp massage have a clear rationale, cost little and carry almost no risk. Mucilage plants for detangling make sense. Gentle, mildly acidic cleansing suits hair better than harsh alkaline washing.

What is worth holding lightly: the stronger claims attached to individual herbs, most of which rest on tradition rather than testing. Tradition is a reasonable basis for a pleasant habit. It is not a substitute for evidence when someone is making a medical claim.