There's a meme floating around the internet that reads: "By Friday, my hair is 90% dry shampoo." And it resonates, right? Since dry shampoo hit the market a few short years ago, people across the country have been singing its benefits, saying things like: "I don't have to wash my hair every day!" and "I can go to the gym without shampooing!"But not everyone thinks the oil-busting spray is a godsend. In fact, many experts are coming out with facts and arguments that may make you rethink your dry-shampoo addiction. Why? It turns out that the cult product can temporarily dull your hair colour, cause undesirable buildup, and even affect your scalp health when used in excess."We've all had that day when we haven't washed our hair for a few days, and it looks good, so I think that's where this belief [that you shouldn't wash your hair every day] came from," says Francesca Fusco , MD, a NYC-based dermatologists.Just because your hair looks good doesn't mean the cause is necessarily a good thing, though, and Dr. Fusco reminds us that regular cleansing is important for the health of the scalp. "When you're cleansing, you're removing dead skin, germs, and bacteria," she says. "You're exfoliating [your scalp], and it's healthier when you exfoliate. When you're using dry shampoo every day, it builds up, and it eventually dulls the hair."Celebrity colourist Rita Hazan echoes this sentiment. "[Dry shampoo] visibly dulls the hair," she says. "Formulas are usually made from aluminium starch or corn starch, which appear matte. This makes the colour in your hair look less shiny and healthy." Hazan says she has seen this turn into a vicious cycle among her clients. She says that since it's common belief that shampooing can dull your color, folks load up on dry shampoo to "save themselves" from that process. Of course, dry shampoo is also dulling the hair, which she says they don't realise.There is also a rumour that shampooing your hair too often will damage your scalp and hair. But is it true? Ken Anderson , MD, founder and director of the Anderson Hair Sciences Centre, says that this idea is completely baseless. "[The scalp] is thicker than the bottom of your heel — kind of like a helmet that's genetically developed to protect your scalp. So the hairs are in there pretty well. They're not just damaged by chemicals on the scalp — they're only damaged by chemicals that penetrate the scalp," he says. Translation: You can, and should, cleanse your scalp regularly.Dr. Anderson also explains that overdosing on dry shampoo can disrupt your hair's natural shedding process. "Like hairspray, [dry shampoo] holds the hairs against your scalp," he says. "If it makes [the hair] sticky, it could tangle the hair, causing you to inadvertently pull some healthy hair out when you brush." It also keeps that shed hair against your head instead of allowing it to fall out naturally. So when you get in the shower, you may see an abundance of hair come out — even though you're not losing any more than normal.At the end of the day, it's a cleanliness issue. "The skin on your scalp is an extension of the skin on your face," Dr. Fusco says. "If your face was oily and dirty, you wouldn't just powder it. You'd wash it." Dr. Fusco also points out that dirty hair is a prime environment for lice and other pests to thrive in.Even Hazan, as a colourist, recommends regular washing. "People with colour in their hair can wash their hair every other day, or even every day, for optimal colour," she says. "At the very least, you absolutely should be shampooing twice a week." Dr. Fusco agrees, and says that as long as you're following your shampoo with a conditioner, you don't have to worry about over-drying. And, you should only use dry shampoo in small quantities — and in a pinch. "Just so long as it isn't taking the place of regular washing, it's fine to use in moderation," Dr. Fusco says. Of course, those with certain hair textures — or dry, damaged, or colour-treated locks — may not feel this applies to them. Obviously, not everyone should be cleansing on the same schedule.So, maybe it's time we shelve our dry shampoo — or at least downgrade it from the star of our hair routine to a recurring guest character. We wash our faces daily, sometimes even twice a day. Why aren't we giving the same respect to our scalps?