# Geraint Thomas Bio

> Science-led platform around skin barrier biology, repair, and evidence-informed communication.


## Posts

- [Phospholipase A₂: Breaking Ground](https://geraintthomasbio.com/phospholipases-and-epidermal-acidity/): When an enzyme releases a fatty acid from a phospholipid, the barrier gains both a lipid chain and an acid group. Follow the inhibitor, knockout and structural experiments that link phospholipases to epidermal acidity.
- [NHE1: Preparing the Ground](https://geraintthomasbio.com/nhe1-preparing-the-ground/): A sodium-hydrogen exchanger in living keratinocytes helps set the acidity around newly secreted lipids. Follow NHE1 from its transport cycle to barrier recovery in mice, then ask how far the evidence reaches in human skin.
- [Filaggrin: The Ultimate Sacrifice](https://geraintthomasbio.com/filaggrin-the-ultimate-sacrifice/): Follow filaggrin through four acts, from a giant precursor stored in liquid-like granules to the small molecules its breakdown releases to hold water and acidify the surface.
- [Hard Water and What Survives the Rinse](https://geraintthomasbio.com/does-hard-water-damage-skin-barrier/): Why should water intended to remove a cleanser help it stay? Follow the rinse into surfactant retention and barrier damage, then test how far that explanation reaches into eczema.
- [The Ingredient Worked in Cells. Does That Mean It Works on Skin?](https://geraintthomasbio.com/in-vitro-skincare-studies/): A cell result shows what happened under the tested conditions. Skin models and human studies ask further questions about delivery, tissue context and product benefit.
- [How Does Skin Know Its Barrier Has Been Damaged?](https://geraintthomasbio.com/how-skin-detects-barrier-damage/): The cells that organise repair lie beneath the surface that has failed. Follow the experiments that exposed the feedback, from changing calcium conditions to three overlapping waves of repair.
- [When Does Urea Stop Being a Moisturiser?](https://geraintthomasbio.com/urea-in-skincare-concentration/): Urea doesn't change its mind at 10%. Its hydrating and keratin-softening effects overlap; context decides which one dominates.
- [Why Does Skin Feel Tight After Cleansing?](https://geraintthomasbio.com/why-does-skin-feel-tight-after-cleansing/): Post-cleansing tightness is the sensory system reading a change in skin mechanics. It reports a physical shift in surface tension, but operates separately from hydration levels or structural barrier failure.
- [Is the Stratum Corneum Dead?](https://geraintthomasbio.com/is-the-stratum-corneum-really-dead/): Corneocytes are dead in the cellular sense, but the stratum corneum is not inert or disposable. Cell death is part of the programme that builds a functional barrier.
- [Does Stinging Mean a Skincare Product Is Working?](https://geraintthomasbio.com/does-stinging-mean-a-skincare-product-is-working/): Stinging means the skin detected an exposure. It may accompany useful activity, but it cannot tell you whether a skincare product is effective.
- [Can Oily Skin Have a Damaged Barrier?](https://geraintthomasbio.com/can-oily-skin-have-a-damaged-barrier/): Oily skin can have an impaired barrier because surface sebum and barrier function are different biological variables. Their coexistence does not prove compensatory oil production.
- [What Does TEWL Actually Measure?](https://geraintthomasbio.com/what-does-tewl-actually-measure/): TEWL measures the rate at which water vapour leaves the skin. It does not measure hydration, diagnose barrier damage or explain why the rate has changed.
- [Why Does Azelaic Acid Sting?](https://geraintthomasbio.com/why-does-azelaic-acid-sting/): Azelaic acid amplifies sensory signalling in the epidermis, creating a noticeable sting. The sensation is a tolerability output, not a diagnosis of barrier damage or proof that the product is working.
- [Does Skin Barrier Repair Take 28 Days?](https://geraintthomasbio.com/does-skin-barrier-repair-take-28-days/): Twenty-eight days is a turnover estimate, not a universal repair deadline. Skin barrier recovery begins quickly, but its different systems do not finish together.
- [Can a Gentle Cleanser Still Disrupt the Skin Barrier?](https://geraintthomasbio.com/can-gentle-cleanser-disrupt-skin-barrier/): A cleanser can feel mild and still alter water uptake, lipid organisation or barrier measurements. The real test is whether the disturbance stays small enough for the skin to recover.
- [Why Petrolatum Works: The Barrier Biology of Occlusion](https://geraintthomasbio.com/why-petrolatum-works-the-barrier-biology-of-simple-occlusion/): The skincare industry frames petrolatum as outdated and 'unbreathable.' The barrier biology disagrees.
- [Drink More Water - Skincare's Most Beloved Non-Answer](https://geraintthomasbio.com/does-drinking-water-help-skin/): 'Drink more water' sounds sensible because it is sensible, just not in the way most people mean it. If the pipeline is broken, sending more water down it won’t fix the pipe.

## Pages

- [Privacy](https://geraintthomasbio.com/privacy/): This site is run by Geraint Thomas, an independent biochemist and writer based in Cardiff. I'm the data controller for anything collected here.
- [Press](https://geraintthomasbio.com/press/): Fact sheet, author bio, quotable copy and downloadable assets for the mechanism-first book on skin barrier biology by biochemist Geraint Thomas. No products.
- [Articles](https://geraintthomasbio.com/articles/)
- [About](https://geraintthomasbio.com/about/): You can understand the chemistry. You can understand the physics. Then you put those rules inside a living system and context starts changing the answer.
- [References](https://geraintthomasbio.com/references/): Academic references supporting The Damaged Skin Barrier, organised by chapter.
- [The Damaged Skin Barrier](https://geraintthomasbio.com/the-damaged-skin-barrier/): Your skin was predictable.
- [Home](https://geraintthomasbio.com/): Geraint Thomas Bio follows questions like these through the biology underneath them.

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