Hair oils are not interchangeable, and I say that as someone who has ended up with a drawer full of them. Some are weightless and glossy, some are richer and better for coarse ends, and some are aimed at a specific shade of hair.

K18's Molecular Repair Hair Oil is the one to try if your hair has been through bleach or heat and needs a light, repair-minded finish. Pureology's Hydrate Glow Catcher is for moisture and shine, and it is the moisture-minded pick. Kérastase's Gloss Absolu Glaze Drops are a drop-by-drop anti-frizz oil, so you control how much goes on. Olaplex's No. 7 Shine Serum is a mist and a treatment in one, and I use it when I want shine without any greasy feeling. Moroccanoil's Treatment Purple Hair Oil is for blonde hair, the one that keeps tone from drifting. Oribe's Gold Lust Nourishing Frizz Reduction Hair Oil is the frizz-reduction option.

A quick test: rub the oil between your palms until it disappears, then smooth over the ends first, never the roots. If hair looks flat or wet an hour later, you used too much. Fine hair rarely needs more than a pea of any oil, and I would rather add a second small application at the ends than start heavy and regret it. Wash day is the time to experiment, since you can always start over. Coarser hair can take double that and enjoy it, which is why I keep both weights around.

An oil makes hair look good. A heat protectant helps it survive the flat iron. They are different jobs, and this is the grid I reach into before any hot tool.

Bumble and bumble's Hairdresser's Invisible Oil Heat Protectant Leave In Conditioner Primer is the one that blurs the line, an oil-feel primer with conditioning built in. Moroccanoil's Perfect Defense is a weightless heat protectant. Pureology's Color Fanatic Heat Protectant Leave-In Conditioner is the color-care option in this grid, and Mizani's 25 Miracle Milk is a milk-style leave-in with heat protection. Olaplex's No. 9 Bond Protector is a serum that reduces frizz while it protects. Oribe's Gold Lust Dry Heat Protection Spray is the spray in the group.

Heat protectants are often designed for temperatures up to 450F, and it is sensible to use the lowest heat setting that gets the style done. Apply evenly and comb through, so no section is missed.

What I would skip: spraying protectant onto hair that is already hot and expecting it to help. It needs to be on the strands before the tool touches them. I would also skip going over the same piece of hair again and again, since extra passes add more damage than any product can offset.

Think in layers. Protect first, style second, finish with oil only where hair needs it. That order keeps hair light and helps you avoid the greasy look that puts people off oils entirely. If a strand feels waxy when you pinch it, take a step back and use half next time.

Match the weight to your hair, and add more only after you have seen how the first amount behaves. Fine hair likes sprays and a few drops of oil, thick or curly hair can take creams and richer oils. Wash out buildup with a clarifying shampoo every few weeks, and let hair rest from heat a few days a week. If your scalp is irritated or hair keeps thinning or breaking, please see a doctor or a trichologist before adding more products.