The folklore that severe maternal heartburn during pregnancy predicts a baby with a full head of hair is a widespread, long-standing belief. This connection between a burning sensation in the chest and a newborn’s appearance sounds like a classic old wives’ tale. However, researchers investigated this piece of pregnancy wisdom to determine if an underlying physiological mechanism links these two seemingly unrelated phenomena. This investigation reveals a surprising intersection of maternal discomfort and fetal development.
The Surprising Scientific Link
The question of whether heartburn severity correlates with newborn hair was addressed in a 2006 study published in the journal Birth. Researchers asked pregnant women to rank their heartburn severity and then independently rated their newborns’ hair volume shortly after delivery. The analysis found a significant correlation between the two factors.
A large majority of women who reported moderate or severe heartburn gave birth to babies with average or above-average amounts of hair. Conversely, most women reporting no heartburn delivered babies with less than average or no hair. This finding suggests a shared biological factor is likely responsible for both outcomes.
How Hormones Affect Both Symptoms
The correlation is believed to stem from high levels of circulating pregnancy hormones, specifically progesterone and relaxin. These hormones rise dramatically during gestation to support the pregnancy and prepare the body for delivery. They have a relaxing effect on smooth muscle tissue throughout the body, including the lower esophageal sphincter (LES) at the base of the esophagus.
The LES normally prevents stomach acid from backing up. As hormone levels increase, the LES relaxes, allowing acid reflux and causing the sensation known as heartburn.
The same surge of hormones that causes this discomfort also modulates fetal hair growth. Progesterone is thought to influence fetal hair follicle cycles, potentially stimulating or extending the hair growth phase. The severity of the maternal symptom thus serves as an indicator of a hormonal environment that promotes a higher volume of fetal hair growth.
What Truly Determines Baby Hair
Despite the hormonal correlation, the quantity, color, and texture of a baby’s hair are fundamentally determined by inherited genetic factors. The genetic code passed from both parents establishes the blueprint for the baby’s hair characteristics. Hair color, for example, is a complex trait influenced by the interaction of genes that regulate pigment production.
Fetal hair growth follows a standard developmental timeline, beginning with the formation of hair follicles around the tenth week of pregnancy. The first hair is a fine, downy layer called lanugo, which typically covers the body and is often shed in the womb between 24 and 28 weeks of gestation. The hair a baby is born with is usually terminal hair, which started growing in the last trimester. Genetics dictates the potential for hair volume, and the maternal hormonal environment may maximize this potential.