Brushing has three modes, and they are doing quite different jobs. The two dry ones are written for straight hair and a loose wave; if your hair curls, or your routine keeps a brush out of it while dry, go straight to the shower section below.

Dry, once a day. Two things are happening here. You are smoothing the surface of each strand so it catches the light, and you are lifting away what the scalp has already shed. Once a day is enough, and not in a hurry — give it about three minutes.

Start at the ends and work upwards in short passes, taking the hair from underneath. If you run the brush down from the roots, the hair stretches and tears where a knot holds it, and that tends to end with scissors. And after washing, put a leave-in on first, or the brush will catch on every small tangle.

If your roots go oily quickly and you are trying to stretch the style to a second day, keep the brush off the skin itself.

Before you wash. Tip your head forward and brush from the nape up over the crown and on towards your forehead, carefully but thoroughly, for about five minutes. That number is a marker rather than a rule; carry on as long as it stays pleasant. The brush has a different job here: it clears the hairs that were going to shed anyway, before they wind themselves through the rest of the length. Oiliness doesn't matter — you are about to wash.

If your hair has started getting dirty faster than it used to, move this to the evening before.

In the shower. Two moments here, and the rules for them are opposite.

Wash the scalp with your fingertips as usual, and if you want a more thorough version of that, take the brush across it with light pressure before you shampoo a second time. The brush reaches across the scalp more evenly than fingers usually manage. Once per wash at most, gently, or the roots will tangle. If a scalp scrub is already part of your routine, keep to the ordinary wash instead of stacking the two. And if your scalp is irritated, or you are shedding more than usual, keep a brush off your scalp altogether for now — dry, before a wash and here — and see a specialist about it.

Once the mask or conditioner is on, keep the brush away from the skin entirely. Separate the hair into sections, touch the teeth to the ends, draw down, then start a little higher and draw down again. That is how the product settles most evenly, and it rinses out cleaner afterwards.

Wet hair wants a brush built for wet hair. An ordinary one does a noticeably worse job in water.