Heart attacks are serious medical emergencies that require immediate attention from a doctor. You could be at risk of a deadly heart attack - or myocardial infarction - if your lips appear to have changed colour, it's been claimed.
Heart attacks are caused by a lack of blood reaching the heart.
Without enough blood, the heart could become seriously damaged - and it may even be life-threatening.
A heart attack could also be a symptom of coronary heart disease, which is where fatty deposits build up in the arteries, which limits the amount of blood reaching the heart.
One of the key warning signs of heart disease, and subsequently a heart attack, is having blue lips.
The colour of your lips is one of the best health indicators, according to Lancaster University's Adam Taylor.
Your lips should remain a red/pink colour, but they can turn blue in some cases.
That may simply be because you're particularly cold, or have been mountain climbing.
But, it could also be caused by the blood struggling to deliver oxygen to various parts of the body.
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"The lips are usually red, but they can take on a bluish colour [cyanosis] in people with heart problems, due to the failure of the cardiovascular system to deliver oxygenated blood to tissues," Taylor wrote for The Conversation.
"Of course, people also get blue lips if they are extremely cold or have been at a high altitude.
"In this case, blue lips are probably just due to a temporary lack of oxygen and will resolve quite quickly.
"If you are worried or in doubt, you should contact your GP or other healthcare professional for an expert opinion."
If you have particularly blue lips or skin, you should go to a hospital straight away, urged the NHS.
The body may not be receiving enough oxygen due to a problem in the lungs, airways or heart.
Meanwhile, you could also be at risk of heart disease if you notice a build-up of yellow bumps on your skin.
These lumps, which are known as xanthomas, may be caused by excess cholesterol in the body.
Meanwhile, the most common heart attack signs include severe chest pain, having a radiating pain in your arm, and suddenly feeling very dizzy.
But you can lower your risk of a heart attack by making some small diet or lifestyle changes.
Eating a healthy, balanced diet will lower your chances of fatty deposits in your arteries.
If you think you, or someone you know, may be having a heart attack, it's crucial that you dial 999 straight away.