What is tetrahexyldecyl ascorbate in skincare?
Tetrahexyldecyl ascorbate – usually shortened to THD ascorbate or THDA – is an oil-soluble ester of vitamin C. Attaching fatty chains to ascorbic acid makes it lipophilic, so it dissolves in the oil phase of a formula rather than the water phase.
That solves two problems at once. It is far more stable than pure L-ascorbic acid, and being oil-soluble it penetrates the lipid-rich barrier more readily. It also works at skin-friendly pH, so it does not sting the way a low-pH vitamin C serum can.
What skin concerns does tetrahexyldecyl ascorbate treat?
Once converted to ascorbic acid in the skin it does what vitamin C does: neutralises free radicals, inhibits tyrosinase to fade pigment, and supports collagen synthesis for firmness and fine lines.
It is a good fit for dry and sensitive skin that cannot tolerate L-ascorbic acid. One caveat from the stability literature is that THDA degrades quickly under some conditions despite its reputation, so packaging and formulation still matter.
What ingredients are best paired with tetrahexyldecyl ascorbate?
Vitamin E and ferulic acid support it as they do any vitamin C, and because it is oil-soluble it sits naturally alongside squalane, ceramides and facial oils.
It layers comfortably with niacinamide, peptides and retinoids, and it is gentle enough to use morning and night. As with all ascorbic acid derivatives, results depend on conversion in the skin, so give it three months before judging. Take our Skin Quiz.
What is melasma?
Melasma is a common form of acquired hyperpigmentation that appears as symmetrical brown or greyish-brown patches, most often across the cheeks, forehead, upper lip and jawline. It develops when melanocytes – the pigment-producing cells in the skin – become overactive and deposit excess melanin into the epidermis, the dermis, or both.
It is far more common in women and in medium to deeper skin tones, and it behaves as a chronic, relapsing condition rather than a one-off mark – which is why management matters as much as treatment.
What causes melasma?
Three triggers dominate: ultraviolet and visible light exposure, hormonal change (pregnancy, oral contraceptives and hormone therapy – hence its nickname, the mask of pregnancy), and genetic predisposition.
Heat, visible light from sunlight and screens, inflammation from harsh products or aggressive procedures, and certain medications all make existing patches worse. Because the triggers are ongoing, melasma typically fades and returns rather than clearing permanently.
What ingredients are best for melasma?
Daily broad-spectrum sunscreen is non-negotiable, and a tinted mineral SPF containing iron oxides is best because it also screens the visible light that drives pigment production.
On top of that, the most evidence-backed actives are tranexamic acid, azelaic acid, niacinamide, vitamin C, alpha arbutin, kojic acid, liquorice root extract, retinoids and gentle alpha-hydroxy acids. Avoid harsh scrubs and strong heat, both of which can rebound the pigment. Take our Skin Quiz to build a routine around your skin tone and triggers.
