L'Oréal Paris Revitalift Filler Hyaluronic Acid Serum (£25) has landed in the UK after a verysuccessful launch in the US; so successful, in fact, that, Stateside, one of these pretty dropper bottles sells every minute. The hyaluronic acid molecule retains a thousand times its weight in water, which, in turn helps to maintain moisture levels in the skin, keeping it feeling super hydrated. This serum (which you can read a full review of here) has been formulated with 1.5 percent concentration, which doesn't sound like a lot, but is actually the optimum amount to hydrate the skin without causing irritation. That means this formula is unlikely to cause any unwanted side effects even in sensitive skin