What causes oily skin, then? "It’s all about the settings on your sebaceous glands and everyone is different," continued Dr Wedgeworth, something consultant dermatologist Dr Anjali Mahto expands on: "Much of it is genetically controlled. We 'inherit' the size of our sebaceous (oil) glands but other risk factors for oily skin include exposure to humid climates, ethnicity and conditions with elevated androgen (male) hormones such as PCOS ." Dr Mahto continued: "People are referring to two different things here. Dehydration is a lack of water in the skin (or increased water loss through the skin barrier), which can occur due to using harsh skincare products and air conditioning, for example. But there isn’t any evidence that oily skin is due to dehydration or lack of water, which is what dehydration really means."