ISDIN Isdinceutics Glicoisdin 25 Intense Exfoliating Peeling Gel Review

Twenty-five is the number on the box and 9.5 is the number that matters. The first is the total glycolic acid by weight; the second is how much of it is left un-neutralised and free to work once ISDIN has brought the gel up to pH 4 to 4.4 with ammonium hydroxide. That distinction is the whole reason a product with a quarter of its formula made of acid can be left on the face overnight rather than washed off after three minutes, and understanding it is the difference between using Glicoisdin 25 Intense well and using it badly. It is not a home chemical peel. It is a very strong daily exfoliant, and those are different things with different rules.

The ladder context matters here more than anywhere else in ISDIN's range. Glicoisdin has been dispensed in numbered strengths by Spanish dermatologists for years precisely so that nobody starts at this rung. The 8 Soft is a cushioned cream for dry skin; the 15 Moderate is the first bare gel, at 6.1% free acid; the 25 Intense is where the sequence ends before you are in a clinic having something applied and neutralised by a professional. ISDIN brought the trio to the US around 2020 and has never marketed the 25 as an entry product, which is honest and also a little unusual for a category where 'maximum strength' is usually a sales pitch.

The formula is the 15 Moderate with the proportions changed. Water, then glycolic acid, now ahead of the denatured alcohol, then ammonium hydroxide in fourth place because neutralising this much acid takes a lot of base. Butylene glycol, aloe leaf juice, a cellulose thickener, a chelator and two food-grade preservatives finish the list. Ten ingredients, no oil, no silicone, no fragrance, nothing that would clog a pore and nothing that would comfort one either. The alcohol is a real presence, a solvent and penetration enhancer that gives the gel its instant dry-down and also its drying edge, and the aloe is a polite gesture rather than a counterweight. This is a formula that has decided what it is and declines to soften it.

Using it is an exercise in respect. On clean, thoroughly dry skin a thin layer stings sharply for a minute, more than the 15 did even after months of adaptation, and the face can stay pink for an hour. In the first week most people flake a little around the nose, chin and forehead, and ISDIN's alternate-night start is the minimum sensible caution; twice a week for the first fortnight suits many users better. Past that adjustment, the payoff is real and specific. Rough, sun-damaged texture on the forehead and cheeks smooths in a way milder acids do not achieve, blackheads and closed comedones clear and stay clear, and the dark marks left by old breakouts fade noticeably faster than they would on their own. That last effect is the one people who persist with this gel tend to talk about most.

The clinical literature supports the strength but is worth reading precisely. A double-blind, vehicle-controlled trial of 8% glycolic acid cream applied twice daily for 22 weeks in women with moderately photodamaged skin found that 76% achieved at least a grade of improvement in overall photodamage versus 40% on vehicle, and described the result as modest and well tolerated. This gel delivers a comparable free-acid dose in a faster-penetrating vehicle, once nightly. Modest and well tolerated is the right expectation at three to five months: better texture, less mottling, a little less sallowness. It is not a substitute for a retinoid on wrinkles and it is not a treatment for melasma, where an aggressive exfoliant on reactive, pigment-prone skin can make things worse.

The drawbacks follow from the design. Dry, sensitive, rosacea-prone and eczema-prone skin should not touch it, and neither should anyone with an active inflammatory breakout, where the alcohol and acid will sting lesions without helping them. It cannot share an evening with a retinoid, salicylic acid, benzoyl peroxide or a vitamin C serum, which for an oily-skinned user already on adapalene means a careful alternating calendar. The jar is a worse container for a runny gel than it was for the cream, with finger dipping and no dose control. And $85 for 50 g of water, acid, alcohol and aloe is a premium that only the labelling discipline and the pharmacy pedigree can explain; the ingredients themselves cost very little.

Who it is for is a short list, and that is not a criticism. Oily or combination skin, already adapted to the 15 Moderate or to a comparable acid, with rough sun damage, textural post-acne roughness or lingering dark marks, and the patience to use it consistently for a season while wearing sunscreen every single morning. For that person, Glicoisdin 25 Intense is a clear, honest, well-specified top rung and it does what it says. For almost everyone else it is a product to work toward, or to skip in favour of the two below it.