Reported by BBC Health
Lucy says she noticed changes in her skin and hair (left photo) alongside symptoms including fatigue and hair loss when her ferritin levels were low. Lighting and shadows also play a part
"Do you have ferritin face?" a young woman asks on TikTok, pointing to dark circles, washed-out skin and brittle hair, alongside before-and-after style photographs. The content creator puts these features down to her iron levels.
It is one of a growing number of videos and posts on TikTok and Instagram claiming that low ferritin - a protein which stores iron in the body - can leave visible clues on your face.
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Users list pale or grey-looking skin, dark under-eye circles, dry or cracked lips, hair shedding and weak nails, while others share portraits claiming stark visual differences.
The phrase "ferritin face" has spread widely across social media, with videos attracting millions of views.
But doctors say appearance alone cannot diagnose iron deficiency.
"Ferritin face is not a medical diagnosis," said GP Dr Aziza Sesay, who is based in the West Midlands. "However, it may be a clue to tell us that something is going on."
Pale skin, hair shedding or brittle nails can accompany low iron, but can also be signs of other conditions, she told BBC News.
Your ferritin levels show how good your body's iron stores are, while haemoglobin is the protein in red blood cells which carries oxygen. When haemoglobin is low, the blood cannot carry as much oxygen - a condition known as anaemia.
But iron stores can become depleted before that happens, meaning someone can be iron-deficient and have symptoms without being anaemic.
"You've got no stored iron but you're maintaining your haemoglobin. That's the big disconnect," said consultant haematologist Dr Drew Provan.
Dr Sue Pavord, also a consultant haematologist, said iron deficiency is common and often under-diagnosed in women.
UK guidelines from the British Society of Gastroenterology say ferritin below 15 micrograms per litre indicates absent iron stores, while below 30 generally indicates low iron stores.
Social media users have shared posts and videos claiming that low ferritin can cause visible changes…