We've all seen the effects of a big night out on our faces - bloodshot eyes, pale, maybe a breakout as your liver works to detoxify.
But a celebrity doctor nicknamed the 'holistic Sherlock Holmes' says your skin might reveal more about your insides than you expect.
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Dr Nigma Talib told The Telegraph she splits sufferers into different groups: 'Dairy face', 'sugar face', 'gluten face' and the dreaded 'wine face'. If you're even a little bit intolerant to something you're eating, all will be revealed on your skin.
"Internal wellness shows up on your face," she told The Telegraph.
"Poor diet can be responsible for lines, wrinkles and a dull complexion or redness."
She says the first thing you'll notice when avoiding certain foods is "the de-puff".
"I was at an event yesterday and met people I hadn't seen for five years, and what I notice is that people start to puff up in the face - that's ageing. So that will go first. And the fine lines and wrinkles, absolutely."
It's not a new theory; 'face-mapping' is an ancient Ayurvedic practice connecting a point on your face to an organ or body part. The theory is by treating your skin internally, you'll clear up externally.
Here are Dr Talib's tips for 'reading your skin'
Looks like: Puffy red cheeks, dark pigmentation patches or spots around the chin.
Gluten is a protein found in wheat, barley and rye. Sensitivity to it will increase the chances of inflammation within the body, including the face. It can also disrupt the immune system and reproductive hormones, resulting in spots or dark pigmentation on the chin.
Try cutting gluten out for three weeks, drinking more water and eating more fibre. The puffiness will soon disperse.
Looks like: Swollen eyelids, bags and dark circles under eyes, small white spots and bumps on the chin.
Dairy sensitivities tend to occur around the chin, which is connected in face-mapping to the reproductive organs.
Try taking a break from dairy for three weeks and see the impact on your face - but be sure to take a calcium supplement.
Looks like: Forehead lines/wrinkles, saggy skin; gaunt and/or a grey look to the face.
Excess glucose molecules attach themselves to collagen, making these normally elastic fibres rigid. Too much sugar impacts the balance of bacteria in the gut, which can also trigger acne on the face, shoulders and chest.
Try cutting your sugar intake in half and gradually weaning yourself off. These symptoms will rapidly decrease.
Looks like: Lines or redness between the eyes, droopy eyelids, feathery lines across cheeks (dehydration), red cheeks and nose.
Alcohol dehydrates the skin, which worsens the look of fine lines and wrinkles. It is high in sugar, which damages the protein collagen that keeps skin elastic.
If your liver is struggling to process alcohol, you might have deep lines or redness between the brows.
Try taking three weeks off alcohol and then enjoying the odd glass of wine one day a week to see a difference in your skin.