A shocking one in 10 Americans get eczema - scientists say they've found surprising culprit in our food

If you're prone to eczema, you may want to lay off the Lays.

A new study has found that salty foods increase the likelihood of suffering itchy flare-ups.

Every one gram extra of sodium consumed per day - the amount in a McDonald's Big Mac - was linked to a 22 percent raised risk of eczema.

Experts believe salt can trigger the growth of staphylococcus aureus, a common type of bacteria that lives on our skin, which scientists believe is responsible for the urge to scratch, leading to skin damage.

Eating just one extra gram of salt a day - the amount in a Big Mac - increases the likelihood of itchy flare ups by 22 percent, scientists from the University of California , San Francisco, found

The skin condition, also known as atopic dermatitis, causes dry, itchy skin and will affect one in 10 Americans at some point in their lives.

Eczema has become more common in recent years, which has pointed to lifestyle factors such as diet. 

It comes as 90 percent of Americans each too much salt, according to the FDA, which recommends that adults limit their daily intake to below 2.3 grams a day.

Researchers from the University of California, San Francisco, looked at data from more than 215,000 people aged 30-70 from the UK Biobank, which includes urine samples and online medical records.

They could tell how much sodium each person was eating from urine samples; and they could see whether people had a diagnosis of atopic dermatitis, plus how bad the condition was, from prescription codes.

Each gram of sodium excreted in urine over 24 hours was linked to 11 percent higher odds of an eczema diagnosis; 16 percent higher odds of having an active case and 11 percent higher chance of a severe case of eczema.

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The researchers also looked at 13,000 American adults who took part in the National Health and Nutrition Examination Survey and found that eating just one extra gram a day of salt - equivalent to half a teaspoon - was linked to a 22 percent higher chance of someone suffering with eczema.

Limiting the amount of salt in eczema patients' diets could help them manage the disease, the researchers said.

'Most Americans eat too much salt and can safely reduce their intake to recommended levels,' said Dr Katrina Abuabara, associate professor of dermatology at UCSF and leading author of the study.

'Eczema flares can be difficult for patients to cope with,' she added, 'especially when they are unable to anticipate them and don't have recommendations on what they can do to avoid them.'

The study was published in the journal JAMA Dermatology.

Eczema is a group of inflammatory skin conditions causing itchiness, dry skin, rashes, scaly patches and infections.

Dermatologists will usually first prescribe creams and washes to deal with the dry skin, and steroid creams to reduce swelling and redness.

If these are ineffective then immunosuppressant drugs, such as ciclosporin or methotrexate, are given. 

These work by inhibiting certain parts of the immune system that drive inflammation, but can negatively affect immunity and the liver.

The condition can intensify to such an extent it becomes debilitating, with inflamed skin all over the body. 

Sufferers may have to endure sensations of burning or have to wrap affected areas in bandages. It can also lead to stress and depression.

It is believed to occur in people with a common genetic mutation that leads to very dry skin. 

Flare-ups of symptoms can also be linked to allergies or triggered by certain soaps or foods.