In 1909, a young chemist named Eugène Schueller started a company in Paris with a mouthful of a name, the French Harmless Hair Dye Company. His first dye was called L'Auréale, after the Auréole, a popular hairstyle of the day. In 1934 the company launched Dop, which L'Oréal describes as the first soap-free shampoo, and in 1939 it took the name it still uses. Hair was the business from the very first day.

That history is useful when you shop, because the L'Oréal shampoo at Sephora is not the drugstore bottle. It is L'Oréal Professionnel, the salon side of the company, and it is organized by what your hair needs instead of by scent or packaging. Once you know your concern, you know your line.

The first grid is the shampoos, one for each line, plus the Metal Detox pre-shampoo treatment. The second is the masks, conditioners and finishing products that match them, so you can build a whole routine within one line.

Here is a test I like for choosing: think about the last time your hair looked bad and name the reason. Rough and breaking means Metal Detox or Absolut Repair. Faded color means Vitamino Color. Frizz means Keratin Alpha Sleek. Thin, split ends mean Pro Longer. Curls that feel dry mean Curl Expression.

Every line here starts with a shampoo, and the right one depends on what is going wrong, whether that is damage, fading color, frizz or curls that have lost their shape.

Metal Detox is the one I would try first if you color your hair. The brand's idea is that metal particles in tap water get into the hair and cause breakage and color shift. The sulfate-free shampoo gently removes them, and the pre-shampoo treatment is a light gel you apply before washing that the brand says gives up to 72 hours of hydration and stops breakage and color shift.

Absolut Repair has two shampoos. The Molecular one is the bond repair shampoo, sulfate-free with bond-building peptides, made for hair damaged by chemicals, color and heat, so think bleach and hot tools. The original Absolut Repair is a moisturizing shampoo with omega 9 and wheat protein for hair that is simply dry.

Vitamino Color Spectrum is for keeping color true. It locks in color, neutralizes unwanted tones and gives a glassy shine.

Keratin Alpha Sleek is the frizz line, a sulfate-free shampoo that smooths the hair and controls volume, good for anyone fighting humidity.

Pro Longer is for long hair with thin, split ends. It thickens the ends so hair looks fuller and longer.

Curl Expression Moisture is paraben- and sulfate-free, made for wavy to coily hair from 2A to 4C, and it removes buildup while it hydrates.

Here is a tip: shampoo the scalp, not the lengths. Let the lather run through the ends as you rinse. That is enough to clean them.

What I would skip: switching lines every wash. Give one line a month so you can see what it does.

Once you have your shampoo, match it. Each line has a conditioner or mask made to work with it, and using them together is how salon products are meant to be used.

For damaged hair, the Absolut Repair Molecular trio works as a set. The rinse-off serum is a quick step after shampoo, with 2 percent peptides, and the brand claims it visibly fights two years of damage in one use. The mask is a weekly step that also detangles. The leave-in conditioner is the finish, a bond-building leave-in that doubles as heat protection before you blow-dry.

For color, the Metal Detox mask keeps metal particles in water from fading color and softens hair, and the Metal Detox hair oil is a light finishing oil that adds shine, cuts frizz and protects color. The Vitamino Color conditioner locks dye into the hair and, according to the brand, keeps color vivid and glassy for up to 100 days.

For frizz, the Keratin Alpha Sleek mask is rich with keratin and leaves hair softer, smoother and shinier right away, with lasting control over frizz and volume.

For long hair, the Pro Longer conditioner is a daily conditioner that strengthens the mid-lengths and thickens split ends so they look less damaged.

Here is a routine I like: your line's shampoo every wash, the matching mask once a week in place of conditioner, and a leave-in or oil on the ends before styling.

What I would skip: trying a new mask for the first time right before a night out. Use it on a quiet evening so you can see how your hair takes it.

I think L'Oréal Professionnel is one of the easiest salon brands to shop, because it tells you plainly what each line is for. There is no guessing, and no need for a dozen products.

If you color your hair, start with Metal Detox: the pre-shampoo, the shampoo and the mask. Use them for a month and notice how your ends feel and whether your color holds. If your hair is damaged instead of colored, do the same with Absolut Repair. Pick one line, stay with it and let the results tell you.