New insight into Alzheimer's disease: Light reverses Aβ-obstructed interstitial fluid flow and ameliorates memory decline in APP/PS1 mice.

•Aβ-inactivated formaldehyde dehydrogenase induces formaldehyde accumulation.•Formaldehyde in turn accelerates Aβ deposition in the extracellular space.•Red light activates formaldehyde dehydrogenase to degrade formaldehyde.•Red light reduces Aβ self-aggregation and formaldehyde-promoted assembly.•Red light recovers interstitial fluid flow and alleviates memory deficits.