Every 37 seconds, someone in the Western world dies from a venous thromboembolism (VTE), where a blood clot forms, most often in the deep veins of the leg, groin or arm.

While clotting is a normal process that can prevent us from losing too much blood when wounded, clots that don’t dissolve can be dangerous, and even life-threatening in some instances.

Blood clots have also become a talking point recently, after the MHRA launched investigations into a potential link between AstraZeneca’s Covid vaccine and a spate of blood clotting events.

To better understand why blood clots sometimes occur and whether you should be worried, we asked doctors to answer some of our most common questions…

What are blood clots and why do they happen?

“Blood clot is a generic term for a thrombosis, which put simply, is an obstruction of a vessel (arterial or venous) by a build-up of platelets and a number of different blood products,” says Dr Emeka Okorocha.

“If a particle of another product breaks off, it gets thicker and travels around the vessels, and may get stuck or create an obstruction. We call this an ’embolism’, which is also a form of blood clot.

“This process could be triggered by an injury, but in some cases blood clots occur inside vessels where there has been no obvious injury.”

What kinds of things put you at risk?

Blood clots can potentially affect anyone, although some lifestyle and genetic factors may put some people at higher risk.

“If you’re obese, bedridden after an operation, have very prominent varicose veins, are pregnant or are on an oestrogen oral contraceptive pill, then you may have an increased risk of blood clots,” says Dr Paul Ettlinger of London General Practice.

They can also be associated with long lengths of time being inactive, and long-haul flights. According to National Blood Clot Alliance, cancer, major surgery, the use of hormone therapy, smoking and being aged over 55 can also be risk factors. Genetic factors may also apply, so it’s important to know your family history.

What are the signs that you might have a blood clot?

It’s not always easy to spot whether you have a blood clot, because the symptoms are different depending on where you think you have it. But there can be some warning signs, especially for deep vein thrombosis (DVT).

“A DVT is commonly found in the leg, so look out for a painful swelling in the calf,” says Ettlinger. “This often happens after a period of immobility, which is why being on a long-haul flight or surgery can often cause an incident.

“Breathlessness and chest pain on breathing can be a sign that a clot has broken off and has entered the lung,” he adds (known as pulmonary embolism).

“But, of course, you can be breathless for lots of other reasons, even a common cold, so beware of any sudden acute onset,” says Ettlinger. This is especially important if you have a risk factor like taking the contraceptive pill, blood clots are in your family history, or if you’re pregnant.

“I’d also look at severe migraines too as a potential warning sign,” he adds.

How are blood clots treated?

“Medical experts often treat blood clots with blood thinning medication, such as anticoagulants,” explains Emeka. “We normally inject the medicine into the patient for a number of weeks, which basically thins the clot and reduces the more severe effects on the body.

“In more severe cases, we use percutaneous coronary intervention (aka a non-surgical angioplasty) to treat blood clots. If a blood clot is caused by something more serious and it has occluded in a vessel, then we can perform surgery. This involves a surgeon entering the vessel, stenting it and removing the clot completely.”

Should we be worried about the Covid-19 vaccine increasing your risk of blood clots?

“While there have been some reports of people suffering blood clots after receiving the AstraZeneca Covid-19 vaccine, the risk is minimal and the benefits outweigh the risk by a long way,” assures Emeka. “With a risk of only four in 1 million, people should not be worrying about developing blood clots following the vaccine and, on the whole, blood clots occur for a number of reasons, including lifestyle factors.”