Oxidised ingredients cause skin damage

Oxidised ingredients cause several types of damage when applied to skin

Free radical cascade — Oxidised oils and actives contain lipid peroxides and reactive aldehydes (like malondialdehyde and 4-hydroxynonenal). These don't just sit on the surface; they initiate chain reactions, stealing electrons from healthy lipids in the stratum corneum and cell membranes, propagating oxidative damage deeper into the skin.

Barrier disruption — The skin's lipid matrix relies on intact fatty acids. When you apply already-oxidised oils, the degraded fatty acid structures can't integrate properly into this matrix. Instead of reinforcing the barrier, they create gaps and dysfunction, increasing transepidermal water loss and sensitising the skin to irritants.

Inflammatory response — Lipid peroxidation products are recognised by the skin as danger signals. They activate NF-κB pathways and trigger pro-inflammatory cytokine release (IL-1α, IL-6, TNF-α), leading to chronic low-grade inflammation even without visible redness.

Protein and DNA damage — Reactive aldehydes form adducts with proteins (crosslinking collagen, damaging enzymes) and can cause oxidative DNA damage in keratinocytes and fibroblasts. This accelerates photoageing and impairs the skin's repair capacity.

Microbiome disruption — Oxidised lipids shift the skin's microbial ecology, potentially favouring pathogenic species over commensals.