Azelaic acid is a stubborn molecule to formulate. It barely dissolves in water, which is why most products containing it are thick creams or gels in which fine crystals are suspended, and why they often feel slightly gritty. Cos De BAHA's AZ15 does something different: it is a clear, watery serum that carries fifteen percent azelaic acid, the same concentration as the prescription gel approved in the United States for rosacea. The trick is on the ingredient list. Sodium hydroxide sits right after the azelaic acid, converting part of it into its far more soluble salt, while propylene glycol, the second ingredient, works as a solvent for the rest. The result is an unusually elegant texture for a high-strength azelaic product, with one open question about how much of the acid remains in its most active form.
That question matters because pH governs how azelaic acid behaves. Neutralising the acid makes it dissolve and feel gentler, but the salt form penetrates the skin less readily than the free acid. Prescription formulations typically keep a low pH and suspend the undissolved acid instead. Cos De BAHA does not publish the pH of AZ15, so it is impossible to say how the finished serum compares, but the design choice leans towards comfort and wearability over maximum potency. For many people that trade-off will be worth it, because the main reason people stop using azelaic acid is itch, sting and a gritty feel on the skin.
The supporting cast is thoughtful and fragrance-free. MSM, listed as dimethyl sulfone and declared at one percent, is an organic sulfur compound often used for its soothing reputation, though evidence for it in skincare is modest. Panthenol, allantoin and dipotassium glycyrrhizate from liquorice are established soothers. Ceramide NP, two forms of hyaluronic acid, betaine and centella with madecassoside add hydration and barrier support. A small group of botanicals, green tea, elderflower, bitter melon and edelweiss, appears near the end. None of these compete with the azelaic acid; they exist to make a fifteen percent serum easier to live with, and that is the right priority.
Azelaic acid itself earns its place on a very short list of multitasking actives with solid clinical evidence. It reduces the acne-related bacterium Cutibacterium acnes, normalises the way cells line the follicle, calms inflammation, and inhibits tyrosinase, the enzyme that drives pigment production. That combination makes it useful for acne, the redness and bumps of papulopustular rosacea, and post-inflammatory dark marks. It is also one of the few acne treatments considered compatible with pregnancy, which is why dermatologists often recommend it to people who cannot use retinoids.
In practice, the serum spreads easily, absorbs within a minute and leaves a slightly tacky film that disappears under moisturiser. Expect a mild tingle or itch in the first week or two, which is normal for azelaic acid at this strength and usually fades with continued use. Starting once a day, as the brand suggests, and then moving to twice daily if tolerated is sensible. Results build slowly: redness and inflamed spots may start to settle within four weeks, while dark marks usually need eight to twelve.
It also combines well with other steps. Azelaic acid and niacinamide target overlapping problems through different mechanisms, so layering a niacinamide serum or moisturiser alongside AZ15 is a common and well-tolerated pairing. With retinoids, the usual approach is to alternate evenings until the skin has adjusted, then use both if there is no irritation. Stacking it with strong glycolic or salicylic acid exfoliants on the same night is where problems tend to start, because all three can cause stinging on their own. For people with rosacea, a plain ceramide moisturiser and mineral sunscreen are the most forgiving companions, keeping the rest of the routine calm while the azelaic acid does its slow work. Photographing the skin in consistent light at the start makes it easier to judge progress after two or three months, since gradual changes in redness and marks are notoriously hard to notice day to day.
There are real limitations. The azelaic acid percentage is declared, but the pH and the proportion that remains as free acid are not, so you cannot be certain this serum performs like a prescription product. The propylene glycol that helps dissolve the acid is a mild irritant and occasional allergen for some people. And, as with any exfoliating active, daily sunscreen is important when treating pigmentation.
Cos De BAHA has built its reputation on inexpensive, single-focus serums sold largely through Amazon and its own stores, and AZ15 is one of its newer, higher-strength launches from 2025. There are few independent reviews so far, which means the long-term tolerance and results in real users are not yet well documented.
The value is striking. At about fifteen dollars for 30 ml on the brand's own US store, and slightly more at other retailers, it costs a fraction of prescription azelaic acid, although the comparison is imperfect because the prescription gel has been proven in large trials and this serum has not. For people with mild acne, redness or dark marks who want to try a high-strength azelaic acid without a prescription, it is a well-designed, fragrance-free, easy-to-use option. Anyone with moderate to severe rosacea or acne should still consider seeing a dermatologist, where prescription formulations and other treatments are available.
