TORONTO -- In a widely-seen video shared on Twitter, actress Alyssa Milano brushes her hair and holds up clumps of her tresses that have fallen from her head.

“I just wanted to show you the amount of hair that is coming out of my head as a result of COVID,” she explains. “One brushing, this is my hair loss from COVID-19.”

Milano has said in earlier social media posts that she first came down with the disease in March and that since then she has had “basically every COVID symptom.” She said she knows she had the disease because she tested positive for COVID-19 antibodies in her blood.

While the wide range of chronic symptoms experienced by COVID-19 patients colloquially known as long-haulers has been well-documented in recent weeks and can include everything from fevers to rashes to body aches, hair loss seems to be a relatively new addition to the list.

However, there has been an increasing number of COVID-19 patients who are reporting dramatic hair loss months after their initial illness.

“It was kind of scary because it was coming out in clumps,” Heather Colton told CTV News during an interview from Belleville, Ont. on Tuesday.

Colton was diagnosed with COVID-19 in March. She said she started losing her hair three months later.

“I was losing it for four weeks and then it stopped,” she said.

Milano and Colton are far from alone.

A recently published report by Indiana University School of Medicine and the Survivor Corps support group compiled data on the most common symptoms experienced by COVID-19 long-haulers.  

According to the results, which have not been peer-reviewed, nearly 500 respondents said they had experienced hair loss.

In another report, published in late July, a dermatologist at the Cleveland Clinic in Ohio said she was seeing patients who were experiencing hair loss two to three months after they had COVID-19.

“I think the timing is really crucial,” Dr. Shilpi Khetarpal said in the report.

WHAT’S BEHIND THE SHEDDING?

Khetarpal attributed the hair loss to a temporary condition called telogen effluvium, which is the result of an abnormal shift in follicular cycling. She said it’s a fairly common condition that involves excessive shedding due to a “shock” to the system.

“There are several common triggers, such as surgery, major physical or psychological trauma, any kind of infection or high fever, extreme weight loss or a change in diet,” she said.

“Hormonal changes, such as post-partum or menopause, can also be a cause. There are other medical or nutritional conditions that can trigger this as well.”

According to the Cleveland Clinic, there are three phases in the hair follicle growth cycle: anagen (growth), catagen (resting) and telogen (shedding). In telogen effluvium cases, the proportion of hair follicles in the shedding phase increases dramatically, up to 50 per cent, which is what leads to mass shedding.

Dr. Sonya Cook, a dermatologist in Toronto, said that hair loss is not uncommon during acute illness because the body prioritizes fighting the virus over growing hair.

“A few months later, the new hair starts to grow and pushes out those hairs that were in the resting phase… and that’s why you get the shed,” she told CTV News on Tuesday.

There is generally a two-to-three month lag between the stressful event and the onset of hair loss in telogen effluvium cases, the Cleveland Clinic said.

“This is why we’re seeing these patients now, several weeks after COVID-19 symptoms resolve,” Khetarpal explained. “Telogen effluvium isn’t a symptom of COVID-19 as much as it is a consequence of the infection.”

Infectious diseases specialist Dr. Abdu Sharkawy, too, said that hair loss can be induced by stress and an immune reaction from a difficult infectious episode. He said it may be too early to know what the exact relationship between hair loss and COVID-19 is at this time.

“Whether this is specifically related to COVID-19 in particular, or simply the immune system having a difficult recovery period after the infection itself is unknown,” he told CTV News on Tuesday.

As for how long the condition can last, doctors agree that it’s usually temporary and shouldn’t cause permanent hair loss.

The Cleveland Clinic said the hair loss can last for up to six to nine months and that most cases resolve themselves on their own, unless they’re related to medication or a nutritional deficiency.

“I think it’s really important to reassure and counsel the patient that this will get better,” Khetarpal said. “Many patients fear going bald, especially women. This hair loss will improve, but it does take time to get back to normal.”