President Donald Trump has been diagnosed with chronic venous insufficiency, the White House announced on Thursday.

Press Secretary Karoline Leavitt shared a letter from Trump’s physician in a news conference, which said Trump was examined after he noticed “mild” swelling in his legs.

Leavitt said the physician described the condition as “benign” and “common,” particularly among adults above age 70.

Leavitt added that the president is in “excellent health” and that the doctor’s full letter would be released soon.

Here’s what you need to know about the condition, what symptoms it causes and how it’s treated.

What is chronic venous insufficiency?

Chronic venous insufficiency (CVI) is a circulatory condition in which the veins in the leg have difficulty returning blood back to the heart due to damaged valves.

“Unlike the arteries, the veins have valves that help return blood to the heart,” Dr. Andrea Obi, vascular surgeon at University of Michigan Health Frankel Cardiovascular Center and associate professor of vascular surgery at University of Michigan Medical School, told ABC News.

She explained that there are larger veins, called deep veins, which return the bulk of blood to the heart, and there are superficial veins, which are just under the skin surface.

“When the valves fail, meaning they don’t adequately return blood to the heart, the blood can back up into the leg, and that’s essentially what venous insufficiency is,” Obi said.

This can cause blood to pool in the legs and lead to leg swelling.

CVI is fairly common, affecting up to 40% of the U.S. population, according to the Society for Vascular Surgery.

Obi said this figure may be an underestimation because CVI is not detected on any routine screening test, and patients often require a duplex ultrasound — a non-invasive imaging technique to assess blood flow and blood vessel structure — for diagnosis.

What are the symptoms?

Obi said most CVI patients have mild symptoms and the most common manifestation is varicose veins, which occur when the blood pools into the superficial veins just under the skin.

The veins become swollen, which can be heavy, uncomfortable or painful for patients.

If patients have CVI in the deeper veins, they may experience leg swelling around the ankle area and it can extend up towards the knee, Obi said.

In more severe cases, darkening of the skin can occur and an open sore or ulcer could develop.

“When the blood pools down near the ankle level, you’ll get discoloration, and it’s a brown discoloration … and that brown discoloration is the result of the iron from the red blood cells that sort of pools there and gets picked up by your immune cells,” Obi said.

Over time, this can make the skin thick and unable to heal from minor trauma, which is when ulcers form, she said.

How is it treated?

Treatments are typically nonsurgical and are mainly to prevent swelling and ulcers from forming, according to the Society for Vascular Surgery.

Obi said if a patient is found to have CVI incidentally and they don’t have symptoms, there is no need for treatment unless symptoms arise.

First-line treatment can include compression, such as wearing compression stockings or an elastic wrap. There are also supplements patients can take to relieve symptoms, Obi said.

“Compression is the very first thing that you prescribe and then, generally, if a patient desires surgical intervention or something like that, you would try compression first to see if they get relief,” she said. “If they’re still symptomatic or not able to live their daily life, then you might proceed down the pathway of doing an intervention to try and help them improve their quality of life.”

If superficial veins are affected, patients may receive vein ablation, which is a minimally invasive procedure to close the veins off, and removal of the varicose veins.

If deep veins are affected, some patients may require an angioplasty to widen the narrow or blocked veins, or stenting to restore blood flow.

Obi said even if someone’s vein valves are prone to failing due to genetics or aging, walking can help overcome this.

“Your calf muscle will substitute for your valves, and your calf muscle will actually push the blood back up to your heart,” she said. “We tell all our patients, ‘You should do some sort of walking program to keep that calf pump strong. The worst thing you can do is stand on your feet for long periods of time and allow the blood to pool.”