If your eyebrows seem to be thinning, the cause might not be cosmetic at all. According to one doctor with millions of followers on TikTok, it could actually be your body signalling a key nutrient deficiency.

The warning comes from Dr Eric Berg, a health expert with more than 2.3 million followers and 30.7 million likes on TikTok, as well as around 14 million subscribers on YouTube. In a recent video he told viewers: “Thinning eyebrows, especially on the outer third is an iodine deficiency.”

This specific pattern is well known in medicine. Doctors call it the 'Hertoghe sign' or 'Queen Anne’s sign', which refers to thinning or loss of the outer third of the eyebrows.

According to Medical News Today, this symptom is often linked to thyroid problems. The outer edge of the eyebrow is the area most commonly affected when thyroid hormone levels are low.

Iodine plays a crucial role because the mineral is needed to produce thyroid hormones. Without enough iodine, the thyroid cannot make sufficient hormones, which can lead to an underactive thyroid and symptoms including hair thinning.

These hormones also control the growth cycle of hair follicles. According to Healthline, low thyroid hormone levels can stop hair follicles regenerating properly, which may lead to hair loss on the scalp and eyebrows.

When hormone levels drop, hairs may enter the resting stage of their growth cycle too early. Experts say this disruption can lead to brittle hair and noticeable thinning along the outer brow.

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Iodine deficiency remains a global health issue despite modern diets. Research cited by World Health Organization estimates around two billion people worldwide may have insufficient iodine intake, although severe deficiency is now less common in developed countries.

The condition can cause a wide range of symptoms beyond hair loss. Fatigue, weight gain, dry skin and sensitivity to cold are also commonly linked to low thyroid hormone levels caused by iodine deficiency.

Dr Berg’s video sparked plenty of reactions from viewers online. One person joked: “I’m deficient in everything.”

“Thin eyebrows but I was a 2000s teenager,” another wrote, referencing the thin brow trend of the era. Several viewers thanked the doctor for highlighting the symptom. One commented: “Thank you so much Dr Berg," while others felt the warning was personal: “Bro called me out,” a viewer admitted.