The Fieldston Science Bulletin

What Makes Hair Red?

By: Cristina Ellis Every Saint Patrick’s Day, we are bombarded with images of red hair. The holiday is mainly associated with Ireland since Saint Patrick is the island’s patron saint; therefore, it is only fitting that in turn, Saint Patrick’s Day is represented by another of the isle’s enduring symbols, red hair. Ireland has a…

Fieldston

May 31, 2025

2–3 minutes

Biology, human-body, Red Hair

By: Cristina Ellis

Every Saint Patrick’s Day, we are bombarded with images of red hair. The holiday is mainly associated with Ireland since Saint Patrick is the island’s patron saint; therefore, it is only fitting that in turn, Saint Patrick’s Day is represented by another of the isle’s enduring symbols, red hair. Ireland has a higher percentage of redheads than any country in the world. Only 2% of the world’s population has red hair, but about 10% of the Irish are redheads. But why do some people have red hair? What is it that determines hair color?

To understand what makes hair red, first, it is essential to understand the composition of hair.. Hairs are thin strands of protein packed into hardened layers. The outer layer (the one we see) is called the cuticle, and its purpose is to protect the softer inner layers, called the cortex and the medulla.

Hair grows out of follicles, which are like small pits in a person’s skin; attached to each follicle is a sebaceous gland, which produces oil to prevent the hair from becoming dry. Hair growth is driven by the dermal papilla (DP), which regulates follicle development and growth cycles.

The dermal papilla interacts with melanocytes, which are specialized cells that produce melanin, the pigment in our hair that regulates color. There are actually two different types of melanin in our hair: eumelanin and pheomelanin. The eumelanin causes hair to appear brown or black, and pehomelanin causes it to look red or yellow.

The relative amounts of these two pigments determine the color of a person’s hair. People with dark hair have a lot more eumelanin in their hair than pheomelanin, and for people with light hair, the reverse is true. But what is it that causes people to have red hair instead of blonde? Once again, it is the level of pheomelanin in one’s hair. While all light-haired people have more pheomelanin than eumelanin, they don’t all have the same amount; redheads have more pheomelanin than blondes.

Hair is one of the human body’s most diverse and compelling parts. It can be used as a form of self-expression or a representation of pride for one’s community. On Saint Patrick’s day, it is used to show pride for one’s Irish heritage and the isle’s long history. If you’re a natural redhead, go out and flaunt it next holiday; if not, well, there’s always box dye.