A quick Google search for “Is Sun-In back in style?” pulls up headlines from last month, last year, and the last decade. Fashion magazines recommended it through the 2010s. Your mom probably used it in the ’80s. For me and fellow elder millennials, it was a middle school gateway to 40-volume bleach. And right now, a new generation of UV enthusiasts (possibly the same ones who are bringing back tanning despite the very well-documented risks of skin cancer) is spraying it in and lying out, waiting for the sun to do its thing.
According to the Spate Popularity Index, which pulls data from Google searches, TikTok views, and Instagram posts, interest in Sun-In is up 32% year-over-year, with another 19% of growth predicted in the next 12 months. Searches about hair-lightening sprays overall are up 61%, with the conversation happening almost entirely on Google, which signals buying intent. Unsurprisingly, the most common related searches are before-and-afters: People want proof the product works before they commit.
But Sun-In’s modern renaissance raises a bigger question: At a time when nearly any beauty goal is achievable with the right tools and tech, why is a $4 bottle of drugstore hair tonic still the product we keep reaching for, especially when the results are far from guaranteed?
How Sun-In works: the good, the bad, and the orange
Sun-In is a hydrogen peroxide-based spray-on lightener that is activated with heat. Spritz it in, go outside, or use a hair dryer, and watch your hair gradually lighten over hours, days, or weeks. The critical caveat is that it usually works as intended only on naturally blonde or light brunette hair. On darker hair, you probably won’t get blonde. You’re most likely going to get red or orange.
“Hair lighteners work by oxidizing melanin. Hydrogen peroxide breaks down the melanin in the hair shaft, and heat activates that process,” explains Izabela Nowak, PhD, a cosmetic chemist and head of the applied chemistry department at Adam Mickiewicz University in Poznań, Poland.
“The orange effect occurs when the pigment is not fully oxidized,” adds Dr. Nowak. “Time in the sun is critical, and so is your starting color. Dark hair contains more eumelanin, which is harder to lift. Full oxidation is less likely to occur, and the result is often warm, reddish pigments rather than true blonde.”
Also on the ingredient list is citrus limon (lemon) juice, which “should help close the hair cuticle after oxidation,” Dr. Nowak explains, in addition to helping lighten on its own. Chamomilla recutita (matricaria) flower extract “has a minor lightening effect [on light hair, not dark]; here, it mostly just adds shine.” And nourishing botanicals like aloe, calendula, and linseed.
It’s worth noting that the “bleach-free” claim on the bottle is, as Dr. Nowak puts it, a half-truth at best. “Hydrogen peroxide is a bleaching agent. While traditional hair dyes usually pair it with alkaline accelerators not present in this formula [those open up the hair shaft, accelerating the dyeing], hydrogen peroxide itself is present. It’s a classic oxidizing agent. This isn’t mentioned at all in the product description.”
Where trends lead, the market follows. While the new class of spray lighteners has yet to achieve Sun-In’s cult status, the competition is real. Standouts include Sun Bum Blonde Hair Lightener ($17), which blends the same hydrogen peroxide base with pineapple and lemon, and Oribe Bright Blonde Sun Lightening Mist ($38), which is explicitly peroxide-free. The formula features lemon, chamomile, and a cocktail of fruit oils and botanicals with added UV protection. “There’s no bleaching effect, and it’s much less aggressive,” brand educator Adam Livermore explained when it launched in 2021. “Think of it like a brightness booster, like getting an extra shot of espresso in your coffee.”
