On 17 August 1988 the FDA approved Upjohn's Rogaine, the first product cleared in the United States for hair loss. Minoxidil had started life as a blood pressure drug, and someone noticed what it did to hair. The New York Times ran the story the next morning. More than three decades later, the brand still says minoxidil is the only FDA-approved topical for regrowth. Everything else on a shelf, mine included, is a different kind of promise.

That is the frame I would put around The Ordinary hair serum. The Multi-Peptide Serum for Hair Density is a leave-in scalp serum, and the brand says it improves the appearance of hair thickness and fullness. Note the word appearance. The Ordinary does not present it as a medical treatment for hair loss, and I like that it does not pretend. What it does show you is the formula, named like a lab report: caffeine, Redensyl, Procapil, Capixyl, Baicapil and AnaGain, with Biotinoyl Tripeptide-1 and Acetyl Tetrapeptide-3 near the top of the ingredient list. The serum has been around a few years, and it sits inside a hair range the brand launched worldwide in March 2022.

The trick is to use it the way the brand describes: a few drops on a clean, dry scalp once a day, ideally at bedtime, and left in. Patch test first. Around it, The Ordinary's Natural Moisturizing Factors + Hyaluronic Acid Scalp Serum is the softer, hydrating partner, and the Glycolic Acid 7% Exfoliating and Brightening Daily Toner is the brand's scalp exfoliant, used a couple of times a week. The 100% Organic Cold-Pressed Moroccan Argan Oil and the 100% Plant-Derived Squalane are for lengths and ends. The Multi-Peptide Lash and Brow Serum, the Eye Serum and the Multi-Peptide + Hyaluronic Acid Serum for Firmness and Elasticity are the same peptide idea for the face.

Start with the question of how your hair is thinning, because it decides what to buy. If it is a slow loss of fullness at the part, a density serum is a reasonable place to begin. If it is sudden, see a doctor first.

Verb's Density Peptide Scalp Serum is the closest cousin to the Ordinary one, and Caudalie's Hair Density Serum is made for all types of thinning. Dr. Groot makes a roll-on, which is the neatest applicator here for anyone who hates dropper mess. Sienna Naturals' Density Nourishing Actives Scalp Serum has nourishing actives in the name, which suits a dry scalp. Dr.FORHAIR's Folligen Thickening Scalp Serum is the one to compare with Dr. Groot's. Nécessaire's Rosemary Serum carries a 70% rosemary blend and 5% Capixyl, and Kérastase's Initialiste is the salon route. Color Wow's Youth Juice Collagen Scalp Serum is the collagen option, and the most playful bottle of the group.

A pairing I like: use only one serum at night. A scalp is skin, and layering three actives is how you get a red, itchy part.

What I would skip: a second density serum on top of the first. Give one a real run of a few months, then judge.

One rule for a thinning shampoo: put it on the scalp, massage for a full minute, and let the suds run down the lengths. The shampoo is really a scalp treatment that happens to be in the shower.

Fable & Mane's Volumizing Shampoo for Fine, Dry, Thinning Hair is the one for hair that is both fine and thirsty, which is a hard combination to shop for. Nécessaire has two, the Rosemary Shampoo and The Shampoo, a scalp cleanse with hyaluronic acid and niacinamide, so you can choose by how your scalp feels. Verb's Density Peptide Shampoo lines up with its serum. Act+Acre's Stem Cell Shampoo and Caudalie's Hair Volume Shampoo are the light, lift-at-the-roots options. Davines' Energizing Shampoo is the energizing one for thinning hair, and Vegamour's GRO Revitalizing Shampoo is the one for anyone already using the brand's serums.

A pairing I like: match the shampoo and serum from the same brand only if you like both. Otherwise mix. The Ordinary serum, left in overnight, works with almost any of these in the morning.

What I would skip: a rich shampoo for fine hair on a day you plan to wear it down and flat. Pick the lighter one.

Try this before buying a tool: two minutes of fingertip massage while the serum is on, small circles, no nails. If you enjoy it, a massager makes the habit stick.

Denman's D6 Detangler and Scalp Massager is the plainest, a detangling brush that doubles as a massager, and it is the one I would put in the shower first. Najeau's Gua Sha Scalp Comb and Fable & Mane's Scalp Massager Comb are the two that combine comb and massage. Briogeo's Scalp Revival Stimulating Therapy Massager, Ceremonia's Scalp Massager and Grande Cosmetics' GrandeHAIR Scalp Massager are the silicone ones for shampoo time. Coco & Eve's Boost Therapy Scalp Massager is the prettiest on a shelf.

BondiBoost's Hair Growth Derma Roller is a different kind of tool, and it belongs in a conversation with a dermatologist before it belongs in your routine. Ask about it, especially if your scalp is sensitive or you use any other active.

A pairing I like: massage the serum in with fingertips, then use the massager only in the shower.

What I would skip: any tool on a scalp that is irritated, or on a scalp where you have just applied an acid toner.

I think The Ordinary serum earns its place as a patient, low drama scalp step. It tells you what is in it, it does not promise a miracle, and it asks for a small habit each night. That is more honest than most bottles.

So I would start with one serum, one shampoo you like and your own fingertips, and take a photo of your part today. If you want regrowth rather than fullness, talk to a doctor about minoxidil, the ingredient that arrived in 1988 and is still the benchmark. Everything else is a good routine. Good routines are quiet. If you want to keep browsing, I also put together What Actually Works and The Best Hair Conditioner Now Does More Than Add Slip.

For lashes and brows instead of hair, I compared the multi-peptide lash and brow serum with a few rivals.