Iron deficiency is more common than any other micronutrient deficiency, according to the American Society of Hematology, yet it can remain undetected for months or years. Fatigue, weakness, brain fog and other symptoms may persist before patients learn that low iron is involved.

A 2024 study found that nearly one third of US adults may be iron deficient. Routine screening for children and pregnant women, both considered at high risk, may miss more than 70% of cases.

Online, some people point to dark under eye circles and pale skin as proof of low iron. Influencers have labeled this supposed appearance “ferritin face,” referring to ferritin, the protein that stores iron in the body.

Dr. Ariela Marshall, associate professor of medicine at the University of Minnesota, described iron deficiency as common, prevalent and underrecognized. New diagnostic recommendations released by the American Society of Hematology in September are intended to help more patients receive earlier treatment.

Anemia occurs when the body lacks enough red blood cells to transport oxygen to organs and tissues. Patients may experience fatigue, dizziness, shortness of breath, heart palpitations, cold hands and feet, pale skin, brittle nails or hair loss.

Iron supports brain and muscle function and helps the body make hemoglobin, the molecule that carries oxygen in blood. When ferritin is low, there may not be enough available iron to produce red blood cells, potentially leading to anemia.

However, iron deficiency can cause similar symptoms even when hemoglobin and red blood cell counts remain unaffected. It may also cause restless leg syndrome and pica, which involves cravings for nonfood substances such as ice or clay.

It is “a common misperception” that iron deficiency without anemia can’t cause symptoms, “and one that we definitely need to correct,” Marshall said. Standard blood tests that count red blood cells will not detect a deficiency that has not progressed to anemia.

“The symptoms of iron deficiency can be very subtle, or they can be attributed to many different things,” said Dr. Jacquelyn Powers, section chief of hematology at Texas Children’s Hospital and lead author of the 2026 guidelines. “Providers are not always thinking, ‘Oh, I need to check iron labs.’”

The amount of iron circulating in blood does not provide an accurate diagnosis because it changes depending on what someone ate and when. Powers said ferritin testing is the gold standard, although laboratories and health organizations have not used one universally accepted threshold.

The World Health Organization recommends a ferritin concentration below 15 ng/mL for diagnosing iron deficiency in school age children and adults. Researchers have questioned whether that threshold is too low and could miss people whose iron stores remain insufficient, while some laboratories use even lower cutoffs.

The new guidelines establish a cutoff of 20 ng/mL or less for children and 30 ng/mL for most adults. The cutoff is 50 ng/mL or less for people with heavy menstrual bleeding or risk factors including a vegan diet or extended antacid use for reflux.

For adults with inflammatory conditions, the new limit is 100 ng/mL, along with an additional test called transferrin saturation. The recommendations emphasize testing for iron deficiency whether or not anemia is present, because interventions can address subtle symptoms and help prevent later complications.

Pale skin, hair loss and dry skin appear in social media descriptions of ferritin face. Powers and Marshall were skeptical that anyone could reliably diagnose low iron from a selfie, particularly because symptoms can vary widely or be absent.

Restrictive diets can make adequate iron intake difficult, but Marshall said diet is not usually the cause of deficiency in the US. Blood loss and digestive conditions are more common causes, while menstruation makes women, especially those with heavy periods, more susceptible than men.

Children and pregnant people face greater risk because growth and development require substantial iron, and deficiency rates among pregnant people rise each trimester. Chronic gastrointestinal conditions, gastrointestinal blood loss and endurance athletics can also increase risk, while declining exercise capacity may signal deficiency.

Powers said checking ferritin is reasonable when someone eats well, sleeps well and follows other habits associated with optimal health but remains tired. Oral iron supplements can ease symptoms within weeks or months, but Marshall stressed the importance of working with a doctor to determine why iron levels became low.