A small strand of hair may seem harmless, but a photo trending on social media this week is proving otherwise.

Scott Walker, a father in Wichita, Kansas, posted this image of his baby's foot, showing one of her toes severely swollen and inflamed, and indicated that the cause of his daughter's pain was a "hair tourniquet."

"Had a small scare this afternoon with Ms. Molly," Walker wrote along with the photo he posted on Facebook on Jan. 21. As of Thursday evening, it had been shared about 37,600 times.

While out to lunch with his family, Walker explained that Molly, who is 5 months old, was "cranky and screaming" and "started to overheat," which prompted his wife to remove the baby's socks to cool her down. That's when they saw something was wrong with her toe.

"This is called a hair tourniquet, which is literally a strand of hair that, while inside a sock, unexplainably wraps around a toe so tight that it can cut through the skin and potentially cut off blood circulation," Walker wrote.

In the medical world, it's more often referred to as ‘toe-tourniquet’ syndrome. According to the American Academy of Pediatrics, the hair, or sometimes a piece of thread from clothing, can become "so tightly wrapped around an appendage that pain, injury, and sometimes loss of the appendage result."

The "tourniquet" causes "lymphatic obstruction, oedema of the tissue and swelling" and a "vicious circle is started as the more the tissue swells, the tighter the tourniquet becomes," according to an article from the Journal of Pediatric Surgical Specialties. Emergency surgery is often required.

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Fortunately, Molly did not lose her toe nor did she need surgery. Her mother was able to remove the hair within a few minutes using tweezers and a magnifying glass, Walker wrote, but not before the hair cut through the baby's skin. (The photo he shared was actually taken 45 minutes after the offending hair strand had been removed, he explained.)

This "strangulation of digits" is a common condition though relatively underreported, according to an article published in the The Royal College of Surgeons of England. And although the most commonly involved parts are fingers and toes, there have been instances where infants' genitals were involved, according to the authors of the article.

Walker said his doctor advised him: "For future reference, to always check the toes if the baby is inconsolable."

And after seeing his cautionary tale go viral, he posted again to Facebook on Jan. 28, writing: "Maybe Molly's tough luck will save a little toe out there someday."