The idea that a mother’s fiery heartburn during pregnancy predicts a baby with a full head of hair is an enduring piece of pregnancy folklore. This belief links a discomforting maternal symptom to a fetal characteristic. While often dismissed as a simple coincidence—since heartburn is common and many newborns have some hair—investigating this notion requires examining the underlying biological processes at work during gestation.
The Truth Behind the Myth
Contrary to expectation, scientific investigation has found a correlation between the severity of maternal heartburn and the amount of newborn hair. A 2006 study tracked 64 pregnant women, examining the relationship between heartburn intensity and the infants’ hair volume at birth, finding a statistically significant association.
Women who reported moderate or severe heartburn were more likely to give birth to babies with average or above-average hair. Conversely, mothers who reported no heartburn delivered babies with less than average hair, or no hair at all. The results suggest the traditional belief is not merely a coincidence, but points toward a shared biological mechanism. Heartburn severity does not cause hair growth, but serves as an indicator of a separate physiological process.
What Causes Heartburn During Pregnancy
Heartburn, or acid reflux, is a common complaint affecting pregnant individuals, particularly in the later stages. The discomfort arises when stomach acid moves backward into the esophagus, causing a burning sensation. This phenomenon is caused by a combination of hormonal and mechanical changes that occur as the pregnancy progresses.
The primary hormonal factor is the increase in progesterone levels, which is necessary to maintain the uterine lining and prevent premature contractions. Progesterone relaxes smooth muscles throughout the body, including the lower esophageal sphincter (LES). The LES is the muscular ring that acts as a valve between the esophagus and the stomach; when it relaxes, it allows gastric acid to splash upward.
Physical changes also contribute, especially in the second and third trimesters. The expanding uterus places upward pressure on the stomach, physically compressing the organ. This increase in intra-abdominal pressure can force acid past the loosened LES. Heartburn symptoms often become more frequent as the pregnancy advances.
The Hormone Connecting Hair Growth and Heartburn
The link between heartburn and fetal hair is explained by the shared effects of high concentrations of certain pregnancy hormones, such as progesterone and estrogen. The same hormones that relax the smooth muscle in the LES also modulate fetal hair development. These hormones circulate at high levels during pregnancy.
The shared biological mechanism involves the dual action of these sex steroids. In the mother, high hormone levels loosen the LES, increasing the likelihood and severity of acid reflux. Simultaneously, these same high concentrations stimulate the growth phase of hair follicles in the developing fetus.
The level of circulating pregnancy hormones acts as the confounding variable, influencing both the maternal digestive system and fetal hair growth. A mother experiencing more severe heartburn likely has a higher concentration of these hormones, which correlates with greater stimulation of the baby’s hair growth cycle. Therefore, heartburn is not the cause of the hair, but a side effect of the high hormone levels that also promote fetal hair growth.