The long-standing belief that maternal heartburn during pregnancy is a sign of a baby with a full head of hair has been a popular piece of folklore. Heartburn, or acid reflux, is a common discomfort where stomach acid backs up into the esophagus, causing a burning sensation. While many old wives’ tales are easily dismissed, this particular one has prompted scientific investigation into a possible biological connection.
Addressing the Myth: Is the Connection Real?
Surprisingly, research has demonstrated a statistically significant correlation between a mother’s report of moderate-to-severe heartburn and the amount of hair on her newborn’s head. A 2006 study found a strong association, suggesting this folklore holds a degree of truth. Of the women who reported moderate or severe heartburn, a large majority gave birth to babies with average or above-average hair volume. Conversely, most mothers who reported no heartburn delivered babies with less than average or no hair. The findings suggest an unexpected link exists, though this does not mean the heartburn itself causes the hair growth.
The Shared Biological Mechanism: Pregnancy Hormones
The observed correlation is likely explained by the dual action of elevated pregnancy hormones, specifically progesterone. Progesterone relaxes smooth muscle tissue throughout the mother’s body to support the pregnancy. One muscle affected is the lower esophageal sphincter (LES), the valve separating the esophagus from the stomach. Relaxation of the LES allows stomach acid to more easily reflux into the esophagus, leading to heartburn.
Concurrently, these same high levels of circulating hormones influence the fetal hair growth cycle by playing a direct role in the development and growth rate of hair follicles. Therefore, a mother experiencing high levels of hormones needed to stimulate significant fetal hair growth would also be more likely to experience the hormone-induced relaxation of the LES, resulting in severe heartburn. This shared biological mechanism, not the acid reflux itself, provides a scientific explanation for the correlation.
Physical Factors Contributing to Reflux
Not all heartburn experienced during pregnancy is solely due to hormonal effects, which explains why some mothers with severe heartburn may not have a particularly hairy baby. As the pregnancy progresses, particularly into the third trimester, mechanical factors also contribute significantly to acid reflux. The growing uterus expands upward, exerting increasing pressure on the stomach and other abdominal organs. This upward pressure physically displaces the stomach, which can force stomach acid back up into the esophagus even if the lower esophageal sphincter is functioning normally. Heartburn primarily caused by this mechanical compression is unrelated to the hormone levels that influence fetal hair growth.