We invited readers on Facebook to ask Real Simple Beauty and Health Director Didi Gluck anything they wanted to about their hair. Here, she answers a selection of those questions.

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Hair dryer and comb
Credit: Gabriella Imperatori-Penn

Q: I’ve noticed that hair product bottle labels always say “for best results,” use a companion product from the same brand. Does it really make a difference?
—Hannah Clay Wareham

A: We get this question a lot—not just about hair care, but also about skin care. The answer is the same in either case: No, you don’t have to strictly use products from the same line. Generally, the suggestion to stick to one line is “clever marketing,” says David Bank, a dermatologist in Mount Kisco, New York. There are, however, some times when you may want to—especially if you’re after maximum efficacy in addressing a specific issue (or you just want the ease of a one-stop shop). For example, say you spend a lot of money getting your hair colored every month; it may make sense to use one line’s shampoo, conditioner, and stylers that all help protect that particular color (for example, John Frieda’s Sheer Blonde line, which is aimed at keeping blondes looking as blonde as possible). Or say you have extremely dry hair; you may want to stick to one line’s hydrating products, which have been formulated to build upon each other (i.e., they deposit hydrating ingredient upon hydrating ingredient on your hair). But if you have normal hair and no specific concerns, mix and match away.

Q: What’s the best product for frizzy, dry, damaged, brittle hair and for keeping my hair sleek against humidity?
—Donna Coleiro

A: I have frizzy, dry, damaged, brittle hair, too! So you’re in luck: I’ve tested just about every frizz-fighter on the market. There are two that I particularly like. One is Fekkai Silky Straight Ironless Smooth Finish Serum ($25, fekkai.com), which is meant to be used on dry hair (just one or two pumps). It’s weightless and really keeps the fuzzy look away even on rainy days. (There’s a corresponding balm by the same name that you can apply to wet hair before blowing it dry, if you really want to fight the good fight.) The other frizz-fighter I love is Living Proof Weightless Styling Spray ($26, livingproof.com). It stops frizz without the use of silicone or oil—the traditional ingredients in anti-frizz products—which some people find too greasy for their hair.

Oh, okay, there’s one more I really like: John Frieda Frizz-Ease Lite Formula Hair Serum ($10, amazon.com). To be honest, the original formula, while life-changing, was too heavy for my hair. This version is, as the name implies, a formula for finer, thinner hair (often a by-product of damage) and won’t weigh it down.

Q: Is there any way to fix split ends or at least make them less visible?
—Yasaman Rad

A: You may not like what you’re about to hear, but, sadly, there is no way to fix a strand of hair once it has split. That said, there are ways of masking the frizzy effect you get from split ends, as well as methods to prevent them.

Start with a clean slate: Get a “healthy” trim (a half inch to an inch off). Then give your hair a little regular TLC: This means using deep conditioner two or three times a week. I love Fekkai PrX Reparatives Intensive Fortifying Mask ($49, fekkai.com). It’s expensive but so effective: I’ve had a tub of it in my shower for more than a year, since I need to use so little with each treatment.

A few other care tips: Don’t use a brush on wet hair; a wide-tooth comb is gentler. Don’t vigorously towel-dry your hair; instead, pat it with an absorbent hair towel. And cut back on shampooing and heat styling: Both can leave hair dry and more apt to split.

Lastly, if you’re having a beauty emergency and need to look less split-ended by tonight, consider a professional blowout. It can make hair appear smoother than your wildest dreams almost instantly.

Q: What is the best after–keratin treatment hair-care tip?
—Rebecca Bellamy

A: I feel like I could write a book on this one, but I’ll try to keep it short.

I have been getting keratin treatments (in a well-ventilated salon, wearing a mask so as not to inhale fumes) for about three years. They are incredible as far as relaxing curls goes, but I did start to notice that after two or three of them (I get about two a year) I reached a point of diminishing returns. Once the keratin started to grow out, my ends looked split and lifeless.

But then my stylist, Paul Labrecque, turned me on to his eponymous Color Shampoo Preserving Hair Wash ($28, paullabrecque.com for info), since I happen to color my hair, too. It’s free of sulfate and sodium chloride, ingredients that can strip away keratin; I also use the matching conditioner ($36, paullabrecque.com for info). The duo has gone a long way toward keeping my hair smooth and shiny. Whether you opt for this shampoo or another, what’s most important is to buy a product that’s free of sulfate and/or sodium chloride (L’Oréal has a whole sulfate-free line). Generally, that’s code for “keratin-safe.” Apart from using the right products, I find tiny but regular trims are a must (every 8 to 12 weeks).

Another suggestion: Ask your stylist to place the keratin starting an inch down from your part. Keratin itself is a moisturizing protein, and all of your hair’s natural oils are concentrated at the root, so the double whammy can actually make this area appear greasy. The slightly removed placement can really improve the overall look of your hair.

Q: What is the best product to use when a perm is growing out?
—Dorothy Borgese

A: Believe it or not, hot rollers or Velcro rollers will be your best friends while growing out your perm. Use them to set your still-warm-from-the-dryer hair while you do your makeup, get dressed, read the paper, or feed the kids/cat breakfast. They’ll maintain the wave pattern you like but on a less permanent basis. Eventually, once you’ve trimmed your ends a few times (and provided you’re deep-conditioning religiously), your curls will be no longer. Then you can choose how to proceed: To perm again or not?

Q: What is the best dry shampoo and how do you use it effectively?
—Pam Shields

A: We road-tested these a while back and absolutely loved Arrojo ReFinish Dry Shampoo ($22, arrojostudio.com). It smells really clean, absorbs oil efficiently, and there’s a lot of it in the can so it lasts. I also really like TRESsemme Fresh Start Dry Shampoo ($5.50, ulta.com) for the same reasons, plus the awesome price.

As for how to use dry shampoo, I have a few tips. While there are different versions (sprays, powders, foams), I favor the sprays because you can best direct where the product ends up. Plus, sprays are lightweight, which is just what you want when your hair is greased down to begin with. Lift small sections of hair with your fingers and spray into roots from about six inches away. Then tousle (as if you’re scratching your scalp) with your fingertips. Style as usual. Or spritz dry shampoo into a ponytail or all over your head (like a hair spray) if your hair is relatively clean, but you just want to build volume and texture.