In January 1807, a London advertisement in La Belle Assemblee offered Macassar Oil, sold by Alexander Rowland of Hatton Garden for the hair. It became so popular that by the 1830s people were covering the backs of their chairs to protect them, and the covers were called antimacassars. Sit with that for a second. A piece of furniture got its own accessory because of one hair oil. Scalp care has never been a small subject.

Two centuries later the question is the same: what goes on your head, and does it help. The answer starts with a diagnosis. The American Academy of Dermatology describes dry scalp as skin losing too much water, with itch and flakes, often set off by harsh hair products, low humidity or cold weather. Dandruff is a different story, and the Cleveland Clinic puts the split neatly: excess oil causes dandruff, and loss of moisture causes dry scalp. A dry scalp treatment is skin care for the barrier, not an anti-dandruff shampoo in disguise.

The trick is to read your flakes first. Tight skin and fine, dry flakes are what leave-on formulas are for, and the first grid is where I would begin. Living Proof makes the Scalp Care Dry Scalp Treatment, a leave-in the brand says is built on a hyaluronic acid Molecular Patch and a vitamin B3 microbiome complex, used on a clean damp scalp three times a week. Act+Acre also leans on hyaluronic acid in its Daily Hydro Scalp Serum. Kérastase has two, the Nutritive Hydrating serum and the Potentialiste, and Moroccanoil makes a Dry Scalp Treatment for people who already trust the brand. OUAI and PATTERN by Tracee Ellis Ross are the lighter serums, easy to fold into a daily habit.

Here is how I would use an oil: before the shower, not after it. Part your hair, put a few drops right on the skin, massage for a minute and leave it while you brush your teeth. Then shampoo it out. The oil softens the scalp, and the wash keeps it from sitting there for days.

PATTERN by Tracee Ellis Ross has a Jojoba Hair & Scalp Oil Blend, the simplest place to start. Fable & Mane makes HoliRoots, a pre-wash treatment oil for scalp and hair, and Act+Acre has a Cold Processed Scalp Detox Oil aimed at dry scalp. Ceremonia's Aceite de Moska is the one with the most personality, and it is called a pre-shampoo oil in its own name, which tells you exactly when to use it.

JVN has a complete pre-wash oil for scalp and hair, and indē wild makes Champi, a pre-wash oil for thinning hair. Sienna Naturals has a Daily Elixir scalp oil and RŌZ makes Willow Glen. All of them turn a rushed wash into a small ritual, which is half the point.

A pairing I like: an oil the night before a wash, then a hydrating serum from the first grid once the hair is clean and damp. Dermatologist James Y. Wang, quoted in Allure, warns against overusing oil-based serums, since too much can encourage yeast. Treat oil as a treatment, not a daily habit.

What I would skip: an oil on a scalp that is already greasy or red. Oil is for dryness, not for every itch.

One rule for a dry scalp: rinse longer than you think. The Cleveland Clinic says dry scalp is usually treated by rinsing shampoo out thoroughly or switching to a gentle, non-medicated shampoo. Two full minutes under the water is an underrated skin care step.

Dr. Groot makes the plain, calm choice, a Scalp Soothing Shampoo for dry scalp. shu uemura offers Delicate Comfort, a clarifying shampoo for dry scalp and hair, which is the one to try if you like to reset without feeling stripped. Crown Affair has The Hydrating Shampoo, my pick for a shelf that also has to look good. Verb Hydrate is written for dry, frizzy hair, and Davines MOMO is another hydrating wash for dry hair.

Kérastase Nutritive is made for medium to thick dry hair, so reach for it if your lengths are as parched as your roots. JVN Nurture is the one I would try if you already like their oil, and Oribe makes a Signature Gentle Daily Shampoo for hydration and shine.

A habit worth borrowing: wash with warm water rather than hot, and see whether your scalp calms down within a couple of weeks. The American Academy of Dermatology lists low humidity and harsh products as common triggers, so a warmer-not-hotter wash is an easy experiment.

What I would skip: a medicated shampoo on a scalp that only feels tight. If flakes are large, oily, or come with redness, that is a dermatologist visit, since dandruff shampoos use different actives.

Start with where the conditioner goes. On a dry scalp the answer is often the lengths only, with a little brushed toward the roots when the skin feels tight. Keep it off the scalp if you tend to get oily by the afternoon.

Two of these are made with the scalp in mind. Moroccanoil makes a Scalp Balancing Conditioner with argan oil, and Oribe makes the Serene Scalp Balancing Conditioner. I would use either if I wanted one conditioner to do a little of both jobs. Nécessaire sells The Conditioner as a hydrating cream, for the person who dislikes a complicated routine.

JVN Nurture, Kérastase Nutritive and Davines MOMO each have a matching shampoo in the third grid, so the line-up is easy to keep together. Fable & Mane makes a conditioner for thick, dry, damaged hair, and Crown Affair has The Hydrating Conditioner, the natural partner to its shampoo.

A pairing I like: a matching shampoo and conditioner from one line, then a leave-on serum only two or three times a week. Fewer moving parts is how you find out what actually helped.

What I would skip: piling every hydrating layer on the same day. When your scalp is feeling better, that is the moment to simplify, not to add.

I think a dry scalp is one of the few beauty problems where less is better. Work out whether it is dryness or dandruff, switch to a gentle shampoo, and add one leave-on serum. An oil before the wash is a weekend treat, not a daily rule.

If the scalp is red, thickened, silvery, painful, or your hair is falling out, see a dermatologist before buying anything. Alexander Rowland's Macassar Oil made a whole century cover its chairs. You only need one serum, one gentle shampoo and a patient few weeks.