Why Foundation “Oxidises” and How to Prevent It

The Cause (Short)
The colour shift is typically caused by air exposure + skin oils/sebum + skin chemistry (including pH) interacting with the foundation’s pigments and base, plus formula factors like volatility and pigment treatment. SCC Online+3Paula’s Choice+3Kryolan+3

The Fix (Short)
Test for dry-down vs oxidation, reduce the triggers (oil/heat/occlusive layers), and pick formulas that stay stable on your skin conditions rather than “going lighter” and hoping it corrects itself.

What most people call “oxidation” is actually two separate processes that look similar on the face. The first is dry-down: the foundation sets as volatile ingredients evaporate and the film tightens, which can make the colour appear slightly deeper or different once it’s no longer wet. Dry-down is normal and predictable and happens even if your skin is perfectly prepped. MatchMyMakeup+1

The second is true oxidation/colour change during wear, which is driven by interaction between the foundation and real-world conditions on skin—most commonly sebum/oil, along with the skin’s chemistry (including pH), humidity, sweat, and air exposure. Industry and skincare sources consistently point to the interaction between skin oils and pigments as a primary driver of foundation darkening/colour shift over time. Paula’s Choice+2Kryolan+2

Formula design matters. Controlled studies show that volatility (how quickly components evaporate) is strongly correlated with darkening over time, and that pigment surface treatment/coating can reduce darkening in silicone-based foundations. Sebum is repeatedly identified as a strong contributor compared with other factors like sweat and light in certain test conditions. PMC+1

Here’s the practical way to diagnose it: apply your foundation and check it at 5 minutes, then again at 30–60 minutes. If it shifts quickly as it dries, that’s mostly dry-down. If it continues to shift later—especially through the T-zone—that’s more likely wear-driven darkening from oil/chemistry. MatchMyMakeup+1

Prevention is about controlling the triggers, not changing undertones. Keep prep thin and fully absorbed, avoid heavy occlusive layers that trap heat and oil, and use thin foundation layers so there’s less pigment sitting in a reactive environment. If you’re oily, blot during wear (don’t keep stacking product), because reducing surface oil reduces the conditions that drive the shift. Paula’s Choice+2SCC Online+2 Finally, don’t confuse “undertone mismatch” with oxidation. Wrong undertone can look like a shift (especially in daylight), but that’s a shade problem from minute one. Oxidation/dry-down is a change after application. Treat them differently and you stop chasing the wrong fix. MatchMyMakeup+1