The No.4 and No.5 pair is the everyday layer: shampoo and conditioner, made for regular washing after the treatments. It is the part of the shelf that actually shows up in your shower three times a week, so it is worth choosing the right version.

No.4 Bond Maintenance Shampoo is for medium hair, and the No.4 Fine version is the volumizing one, which is my answer if hair goes flat the moment it gets wet. The Olaplex shampoo in either version is the everyday wash, made for regular use between treatments. No. 4C is the clarifying one. It removes buildup, so I use it every few weeks, and after a pool day, before I do a deep treatment. It is the reset button when everything starts to feel coated.

No.5 Bond Maintenance Conditioner comes in a medium and a fine version, matching the shampoos. Match them: a fine shampoo with a heavy conditioner will undo the point. I like to use a wide-tooth comb here so the product reaches every strand. Comb conditioner through mid-lengths and ends, leave it for a couple of minutes, then rinse with cooler water for shine.

No.4D Clean Volume Dry Shampoo is the between-washes helper, a weightless detox dry shampoo for roots. It is good on day two, and good when you are traveling and do not want to wash. Just brush it through so it does not sit on the scalp.

Olaplex is far from the only name in the conversation, and it is worth knowing what else people reach for. These are all bond-building or strengthening products, and they behave differently from one another.

K18 Biomimetic Hairscience Leave-In Molecular Repair Hair Mask goes on damp hair and stays in. It is quick, and there is little to rinse, which suits mornings when you have ten minutes. Kérastase Première is a pre-shampoo treatment, so you use it before you wash, and it suits tired lengths. shu uemura Ultimate Reset is a rich mask for very damaged hair, best on a weekend. Oribe Hair Alchemy is a serum that works as a strengthening treatment, and L'Oréal Professionnel's Absolut Repair Molecular mask is another bond-focused option. Bumble and bumble Bond-Building Repair Conditioner is the easiest swap for anyone who wants their normal conditioner to do a little more.

What I would skip: stacking three of these in one wash day. More is not better with bond builders, and too many layers can leave hair heavy, stiff or coated. Pick one treatment per wash, watch how your hair feels for a few weeks, and keep a note of what changed. If breakage is sudden or scalp irritation appears, ask a stylist or a doctor before adding another product.

Here is how I would run it. Treatment first if you use one, then your shampoo, then conditioner, then a styler with heat protection, and only on wash day.

Start with a single number and add slowly, so you can tell what is actually making the difference, and resist the urge to buy the whole line in one go. A note on your phone with the date and product is plenty. Use clarifying shampoo sparingly, and keep tools on a moderate heat setting, since no product fully forgives a very hot iron. Trim ends on schedule, because a treatment can improve how hair feels, but it cannot rejoin a split. And if your hair keeps snapping, get a stylist to look at it in person. Sleep on a smooth pillowcase, detangle from the ends up while conditioner is in, and let hair air-dry now and then. Those small habits protect whatever the numbered bottles are trying to do.