The human body is covered in two main types of hair: fine vellus hair and thicker, darker terminal hair. Scalp hair is terminal hair, but the hair that develops in the pubic region exhibits a dramatically different texture. This contrast, from the smooth strands of the head to the stiff, coiled texture below, is due to the unique structure of the hair shaft and the follicle from which it grows.
The Structural Difference in Hair
The coarseness of pubic hair is a direct consequence of its specialized physical structure compared to scalp hair. The hair follicle determines the final shape of the hair strand. Follicles that produce straight scalp hair are typically round in cross-section, but pubic hair grows from an elliptical or oval follicle. This shape forces the shaft to flatten as it emerges, and this flattened cross-section dictates the hair’s curl and stiffness.
Pubic hair possesses a larger diameter, making it one of the thickest hairs on the human body. This increased thickness is supported by the presence of a central core called the medulla, a dense, irregular structure absent in many finer hair types. The combination of a large diameter, the medulla, and the flattened, coiled shape gives the hair its characteristic rigidity and springy, coarse texture. These structural attributes provide the hair with greater mechanical strength.
Hormonal Influence on Texture
The development of this specialized, coarse hair is controlled by biological timing and chemical signals. Pubic hair is classified as ambisexual hair, meaning its growth is stimulated in both sexes by the rise of sex hormones during puberty. The main biological trigger is the increased production of androgens, such as testosterone and dihydrotestosterone.
Hair follicles in the pubic region are sensitive to these circulating hormones. Androgens signal the vellus hair follicles, which previously grew fine, short hair, to transform. This hormonal instruction initiates the growth of deeply penetrating terminal follicles that produce the larger, darker, and more durable hair recognized as pubic hair. The process marks a clear biological signpost of sexual maturation.
Evolutionary Functions of Coarseness
The coarse, highly coiled texture of pubic hair serves several adaptive functions developed over human evolution. The dense, springy network of hair acts as a layer of cushioning to reduce friction between skin surfaces during vigorous movement or sexual activity. This protective barrier helps prevent chafing, irritation, and micro-trauma to the sensitive genital skin.
The coarse, curled structure is an effective trap for chemical signals produced by the body. The pubic region is rich in apocrine glands, which secrete an oily, odorous substance; the hair’s texture helps to hold and disperse these secretions. These secretions contain pheromones, serving as a subtle form of sexual signaling to potential mates. The presence of this coarse hair aligns with the timing of its development during adolescence.