Can you downshift your sun cream? £5 Nivea vs £3 Aldi, £18 La Roche Posay vs £8 Ambre Solaire & more

Downshifting is practically in our DNA at MSE, so naturally we want to avoid damaging said DNA by blocking harmful UV rays with sun cream... but it can be expensive. So I set out to find whether downshifting sun cream is possible, and asked skin experts about safety.