Scalp care glossary

The skin covering the top, sides, and back of the head. It has the same two layers as the skin on the face, with a layer of fat beneath them. What sets it apart is the hair, and each follicle has its own oil gland. Every hair on your head grows from within a follicle in it.

The skin's own oil, made by the gland beside each follicle. It keeps the skin and hair from drying out. Too much on the surface is what makes roots feel greasy within a day of washing.

The gland that makes sebum. On the scalp, one sits beside nearly every follicle, which is why the scalp is one of the oiliest areas of skin on the body.

An accumulation on the scalp of oil, dead skin cells, sweat, and residue from hair products. It makes the scalp feel heavy or waxy and can flake. It is removed by washing; it is not a condition.

The outermost layer of the skin, which holds water in and keeps irritants out. Harsh washing and stripping products weaken it; a weakened barrier feels tight, dry, or itchy.

The technical name for the very top layer of the epidermis: flattened, dead skin cells that form the barrier. It renews from below and sheds from the top continuously, on the scalp as everywhere else.

A measure of how acidic or alkaline something is, on a scale where 7 is neutral and lower numbers are more acidic. Skin sits on the slightly acidic side. The Scalp Tonic, a leave-in, is formulated to pH 4.5 to 5.0, slightly acidic as well.

The community of microorganisms, bacteria and yeasts, that lives on the scalp's surface, as on all skin. It is normal and present on every scalp. This is a definition; whether a cosmetic changes it is not something a cosmetic may claim.

A light, water-based liquid applied to the skin of the scalp and left there. Lighter than a serum, never oily. The word is not a regulated category; it describes texture and purpose.

A heavier, more concentrated leave-in for the scalp, often applied in smaller amounts to specific areas. Cosmetic, like a tonic. The border between the two is texture, not regulation.

Any product designed to stay on the skin or hair rather than be rinsed. Tonics, serums, and some oils are leave-ins; shampoos and scrubs are rinse-offs. Rinsing a leave-in removes it before it has done its work.

An ingredient that draws water into the skin and holds it there. Glycerin and panthenol are common examples. Humectants are why a leave-in can make a tight, dry scalp feel comfortable.

A family of mild, large-molecule acids used in skin care. Gluconolactone, the one in the Scalp Tonic, is a form of gluconic acid, which also occurs naturally in honey. Because the molecule is larger than glycolic or lactic acid, it stays closer to the surface and is gentler on skin. At the level used here, and at the Tonic's pH, which sits close to the scalp's own, it works as a softening, water-binding conditioning agent and helps the formula stay fresh. It is not there to exfoliate.

A branded ingredient sold as a ready-made blend: the active molecules in a carrier such as water, glycerin or glycol. When a formula uses a complex at 3%, the 3% is the blend, not the pure molecule. The Scalp Tonic carries two, Procapil™ and Redensyl™, at 3% each.

The International Nomenclature of Cosmetic Ingredients: the standard names that appear on an ingredient list, in descending order of amount. Reading the INCI list is the most reliable way to know what is in a product. The Scalp Tonic's full list will be printed on its label; ask and we'll send it to you.