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 dry skin?
Dry skin – xerosis in clinical terms – is a skin type that lacks oil rather than water. It feels tight after cleansing, looks flaky or rough, may show fine cracking, and often reads dull because the uneven surface scatters light.
It is worth separating dry skin from dehydrated skin: dryness is a lack of lipids and is usually lifelong, while dehydration is a temporary lack of water and can happen to oily skin too. Many people have both at once.
What causes dry skin?
At the root is a compromised moisture barrier. When ceramides, cholesterol, fatty acids and natural moisturising factors run low, water evaporates out of the skin faster than it can be replaced.
Age, genetics, cold weather and low humidity, long hot showers, harsh surfactants, over-exfoliation, some medications, and conditions such as eczema and psoriasis all deplete those lipids. Consistent moisturising is the single intervention with the strongest evidence behind it.
What ingredients are best for dry skin?
Rebuild in layers. Humectants such as hyaluronic acid, glycerin, urea and panthenol draw water in; emollients such as squalane, jojoba oil and shea butter smooth the surface; and occlusives seal the whole thing in.
Ceramides, cholesterol and fatty acids are the priority, because they replace exactly what a dry barrier is missing, with niacinamide helping the skin make more of its own. Apply to damp skin, and swap foaming cleansers for cream or oil-based ones. Take our Skin Quiz to find the right combination for your skin.
