How Dry Shampoo Works, According To Science

Dry shampoo is one of those super convenient beauty tools we really couldn’t imagine living without, especially since it comes in handy on all those dirty ‘do days, when our locks need a well-deserved break. But while a spritz of your go-to formula can instantly save you from a bad hair day, most of us are probably stumped when it comes to understanding how dry shampoo actually works.

Now, you don’t exactly have to be a scientist to understand that dry shampoo combats oiliness with absorbent products, but it’s more than helpful to know what exactly goes inside your trusty sprays and powders. That way you can find the product that works best for you.

“Dry shampoo formulas contains silica, which is an absorbent fine powder,” says Alterna Product Development Director, Catherine DeCeglie, via email. “When the powder is applied onto a wet, oily or dirty surface, it absorbs anything on the surface — similar to a sponge. Once those little sponges absorb the oils and dirt, they become heavier and can be brushed out, leaving a refreshed surface behind.”

To find your best dry shampoo match, let's break down everything you need to know about your favorite formulas. Here’s exactly how dry shampoo works according to science.

1. What's Inside

Dry shampoo formulas, which generally come either in spray or powder form, work to sop up the hair’s superficial grease, making your tresses look and smell fresh and matte. But to really understand what makes dry shampoo unique, it's important to understand your formula's ingredients, as brands utilize different components to ensure refreshed-feeling strands. 

“To understand why dry shampoo works, you have to understand what the ingredients are all about,” says Dr. Michael Zasloff, Chief Science Officer of the illumai hair brand via email. “Most dry shampoos have a propellant, an absorbent, and an abrasive, which work together to make your hair look and feel cleaner.”

Looking at the first component of dry shampoo, the propellants (butane, isobutane, propane, alcohol, etc.) work to blast your ingredients evenly throughout the hair. This is crucial, since using you are not using water.

Next comes active ingredients like aluminum starch and silica, which mop up any moisture and oily films that cover the hair. Dr. Zasloff states that the particles of starch act both like little sponges and scouring pads, working to absorb the grease and oil prevalent on your roots.

“When the shampoo is first blown onto the hair, the starch particles act as sponges,” adds Dr. Zasloff. “When the starch is brushed out, they act as scouring pads, being swept across the surface of the hair shafts.”

2. Ingredients To Avoid

But while oil-absorbing ingredients help to keep your hair matte and oil-free, some ingredients can have some precautions to keep in mind. Talc and aluminum starch octenylsuccinate for example, are often avoided by health-conscious consumers, being that they’ve been linked to harmful health conditions. However, not all dry shampoo formulas use such ingredients, as some brands use natural rice starches instead. 

“While these ingredients are not harmful to your hair or general health, many health-conscious consumers lean away from these ingredients in their beauty routines,” says Heather Coughlin, Director of Product Development for amika, through email. “amika’s Perk Up Dry Shampoo does not contain either of these ingredients, and instead uses natural rice starch to achieve the same effect.”

3. Where To Spray

It’s true that there are many dry shampoo formulas on the market, but aerosol sprays tend to be the most popular, as they can tackle greasiness on the spot. But while spray-and-go formulas can conveniently work in seconds, sometimes the application part gets tricky. For best results, Heather Coughlin recommends spraying your roots and waiting before brushing. This allows your formula to work its magic, removing any excess oil prevalent in the hair.  

“To get the maximum benefit of any dry shampoo, lightly spray the root area, and wait approximately two minutes," explains Coughlin. "This allows the formula to absorb any excess oil and environmental debris in the hair." 

Next, Coughlin recommends brushing your formula throughout the hair, to ensure that your formula is evenly distributed. But if you really want to take your dry shampoo game to the next level, Coughlin recommends spraying some dry shampoo formula onto your hair before bedtime, as it will leave your hair fresh and voluminous the next morning.

“For an added benefit, apply dry shampoo at night before going to bed,” Coughlin adds. “Incorporating dry shampoo into your nighttime regime beats oil to the punch, and guarantees voluminous and fresh strands in the morning.”

4. How Much To Apply

There are many dry shampoo formulas to choose from, but a successful application is more about "how much" than "which one." "If you have fine hair, you will only need a light spritz of dry shampoo to soak up excess and amp texture and volume," Nick Arrojo, founder of Arrojo Studiosays through email. "Conversely, anyone with thick or coarse hair will need to use a much heavier application." 

In addition, Arrojo tells me curly and straight hair types differ greatly when it comes to dry shampoo application. Curly hair types in particular should be extra cautious when using dry shampoo products. 

"Those with naturally curly texture should apply the product differently to those with straight hair," Arrojo says. "Straight and regular types can apply lots of dry shampoo into the roots and shake and tousle the hair,  but curly hair types need to be much more judicious with their application. On curly hair, dry shampoo can expand the shape too much, making it too wild and out of control." 

5. How Often To Use

Dry shampoo fans have a tendency to overuse the product, relying on it most days a week to keep their hair looking fresh. Bad idea, apparently.

Tina Hedges, Founder of LOLIBeauty, finds that overuse of aerosol sprays can clog hair follicles, and disrupt the balance of a healthy scalp. In addition, Dr. Zasloff adds that too much use of starch and silica based formulas can wear away at the surface of the hair shaft, causing breakage you won’t want to deal with.

“The grittiness of the starch and silica physically wears away the surface of the hair shaft,” says Dr. Zasloff. “Using this option on a regular basis can damage your hair, wearing it away until it becomes fragile and breaks.”

In order to keep your hair safe, stick to dry shampoo just a couple days a week, and never apply more than you can brush in. 

6. How To Make Your Own

Drugstore dry shampoos are easy to find, but homemade dry shampoos can be a good alternative if you're not about chemicals. 

To make your own dry shampoo, Hedges recommends using a powdery base, like a mix of arrowroot and yucca. Then, add in some drops of essential oils for a pleasant aroma. However, keep in mind that there is no set rule book on how to make your own formula, especially since Hedges says there are many ingredient combinations you can try out.

“Feel free to mix and match ingredients to meet your own specific needs,” Hedges explains via email. “Let’s say you have dark brown hair, you can add in a bit of cocoa or clove powder to blend with your hair color. Or maybe you have an itchy, flaky scalp, you can add in a few drops of rosemary, thyme and chamomile essential oil.”

7. When To Use Your Regular Shampoo Instead

While dry shampoo definitely is a lifesaver,  it really shouldn’t replace shampooing altogether. Unlike shampoos, dry shampoos don’t contain surfactants, which means they don’t work to clean the scalp and the hair. And after two to three applications, chances are your hair will feel heavy and tacky from all the product application.

“Once you’ve applied dry shampoo about three times in an attempt to prolong your blowout, it is probably time to wash your hair for real,” says skincare expert, Tsippora Shainhouse via email.

Of course dry shampoo allows you to give heat styling and shampooing a break, but shampoo is still needed to remove dirt, sweat and residue from your scalp, as hair care products like dry shampoo can lead to unwanted definitely build up. Now, you can still use dry shampoos when you want to give your hair a break, but experts like Shainhouse recommend still using shampoos to remove yeast and bacteria from the skin’s surface.

“Shampoo removes the excess grease and sebum from your scalp, and helps clear your hair follicles, so that your hair can grow out healthier, and so that your scalp can actually regulate its natural oil production,” Shainhouse says.

But as long as you hop in the shower a couple times a week, dry shampoo can continue to be the miracle product we've all come to love. 

Images: michael_fertigfadequmarkoukrainianmili_vigerovataravernehojayjay08szolkin/Unsplash 

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