A widespread piece of pregnancy folklore suggests that experiencing severe heartburn during pregnancy is a prediction that the newborn will have a full head of hair. This connection between the burning sensation in the chest and an infant’s hair volume seems unlikely, positioning it firmly in the category of old wives’ tales. However, this enduring belief prompts a scientific investigation into whether this correlation is merely anecdotal or if a shared biological mechanism actually links the mother’s digestive discomfort to the baby’s hair development. The answer provides a look at how the body’s internal chemistry connects two seemingly unrelated experiences during gestation.
The Physiological Causes of Pregnancy Heartburn
The primary cause of heartburn in pregnancy is rooted in the increased levels of hormones that circulate throughout the body. The hormone progesterone, which is produced in high amounts to support the pregnancy, has a relaxing effect on smooth muscle tissue. This smooth muscle relaxation includes the lower esophageal sphincter (LES), the muscular valve situated between the esophagus and the stomach.
Normally, the LES closes tightly after food passes through to prevent the acidic contents of the stomach from flowing backward. With the relaxing effect of progesterone, the LES pressure decreases significantly, allowing stomach acid to reflux more easily into the esophagus, which creates the burning sensation known as heartburn. Additionally, the physical growth of the uterus puts increasing pressure on the stomach, particularly in the later trimesters. This mechanical pressure further exacerbates the reflux by pushing stomach contents upward toward the weakened esophageal sphincter. The combined effect of hormonal changes and mechanical pressure makes heartburn a common experience for many pregnant individuals.
The Myth Debunked: Heartburn Severity and Fetal Hair Growth
Scientific research has found a significant correlation between the severity of a pregnant person’s heartburn and the amount of hair on their newborn. A study published in 2006 by researchers at Johns Hopkins found that among the participants who reported experiencing moderate or severe heartburn, the majority gave birth to babies with an average or above-average amount of hair. Conversely, most of the participants who reported no heartburn at all had babies with less than average or no hair.
This research indicates that the old wives’ tale is not just a coincidence but an observation of a genuine association. The study found a relationship between the reported severity of the heartburn symptom and the independently rated volume of the newborn’s hair. This finding suggests that if a pregnant person is experiencing significant acid reflux, the likelihood of their baby having a noticeable amount of hair at birth is higher. This correlation does not mean the heartburn itself causes the hair growth, but rather that both phenomena are linked to a shared, underlying biological process.
The Hormonal Bridge: Why the Correlation Exists
The shared biological mechanism that creates this correlation is the elevated level of pregnancy hormones, primarily estrogen and progesterone. These hormones act as the “hormonal bridge” connecting the mother’s digestive discomfort to the baby’s hair growth. Progesterone and estrogen are responsible for maintaining the uterine lining and supporting fetal development, but they also have widespread effects on other body systems.
The same high concentrations of progesterone that cause the relaxation of the lower esophageal sphincter, leading to heartburn, are also believed to play a role in the fetal hair growth cycle. Researchers hypothesize that the hormones stimulating fetal development, including the transition of hair follicles into their growth phase, are the same ones that cause the smooth muscle relaxation in the mother’s esophagus. Therefore, a pregnant individual with higher levels of these hormones is more likely to experience severe heartburn due to the relaxed LES and simultaneously carry a fetus whose hair development has been significantly stimulated. The severity of the heartburn simply acts as an indirect indicator of the hormonal environment that also promotes a full head of hair on the baby.