It may seem counter-intuitive to apply oil to already oily skin, but trust us on this one. If your skin is producing excessive amounts of sebum, it's very likely trying to compensate for underlying dryness. The solution is to hydrate your skin regularly. Sunday Riley's U.F.O. Ultra Clarifying Oil (£34) contains one and a half percent salicylic acid to battle acne and skin congestion while milk thistle and cucumber seed oil nourish, hydrate, soothe, and plump.