This photo was taken as part of the Dutch festival of Internationale Roodharigen Dag, or International Redhead Day, in 2011. Note the huge variety of straight, wavy, and curly or kinky hair styles and types that are represented here. (Credit: Qsimple/flickr)
Whether your hair is straight, wavy, curly, or kinky isn’t just genetic in nature. It depends on the physics of your hair’s very atoms.
Across the animal kingdom, hair and fur are exceedingly common.
Although these alpacas are all covered in fur, the thickness, curliness, and length of the fur varies from animal to animal and from location to location within an individual animal. The size and shape of the hair follicle plays a role, but the molecular protein structure of the keratin fibers composing the hair or fur of an animal is the main culprit. (Credit: Antanasc/Goodfon)
They come in many varieties of thicknesses, styles, and structures.
The emperor tamarin monkey is notable for its facial hair, which typically curls downward in a set of long, low-looping arcs, although there are exceptional examples that possess alternative features. Its hairstyle is determined by the bonds that occur in the protein structure of its keratin. (Credit: h080/flickr)
Despite these varied properties, hairs are generally similar.
Various thicknesses of skin are found on varying locations on the human body, and often correlate with the level of hairiness of that region. Your armpits have particularly thin skin, whereas your knees have relatively thick skin. Skin thickness also varies by age, health, and other factors. (Credit: Madhero88 and M.Komorniczak/Wikimedia Commons)
For all animals, it’s composed of keratin: a protein-based structure.
This diagram shows the structure and the various structural elements of the keratin found in hair. Keratin, despite its complexity, is just a protein at its core. (Credit: W. Zhang & Y. Fan; Methods in Molecular Biology vol. 2347, 2021)
All proteins, in turn, contain amino acids as building blocks.
