Shampoo Day

What the day is

Shampoo Day is observed on October 20. It marks the product and the routine, both of which are more recent and more contingent than they feel.

Origin and background

The origin of the observance is not documented. The word's origin is well recorded: shampoo comes from the Hindi champo, an imperative meaning to press or massage, and it entered English through colonial contact in the eighteenth century. It originally referred to a vigorous head massage rather than to any cleaning product, and the meaning shifted to the soap itself during the nineteenth century.

Before modern shampoo, hair was washed infrequently with soap, which reacts with minerals in hard water to leave a dull film. Synthetic detergents in the twentieth century solved that, and the industry then had a product people used perhaps weekly and a strong commercial interest in more frequent use. The instruction to lather, rinse and repeat is the most quoted artifact of that period.

The science is less dramatic than either the marketing or the backlash. Shampoos clean with surfactants, molecules with a water-loving end and an oil-loving end, which lift sebum and dirt so water can carry them away. Stripping too much oil prompts the scalp to produce more, which is the kernel of truth behind claims that washing less often trains the hair, though the effect is modest and varies enormously with hair type.

The right frequency genuinely differs. Fine, straight hair shows oil within a day; tightly curled hair is often drier and can go a week or more, and over-washing it causes real damage. Most of the internet argument comes from people generalizing from their own scalp.

How to take part

• Wash the scalp rather than the lengths. The ends need conditioner, not detergent.
• Skip the repeat unless your hair is genuinely dirty. Once is usually enough.
• Use lukewarm water; very hot water strips more oil and does nothing extra.
• Rinse considerably longer than feels necessary. Residue is a common cause of dull, itchy scalps.
• Match the product to your hair rather than to the packaging, and change the frequency rather than the brand if something is wrong.