One of the matters you may wish to consider in any world-building you do are scars, both physical and psychological, and both on a personal level and on the level of your society.
You can milk a scar or a collection of scars for a lot of characterization. Did the person have a disfiguring childhood disease? Were they beaten or flogged as punishment for something? Did that very sedate, almost passive character have a violent youth?
Keep in mind that how the scars were gotten and how the character *says* they were gotten aren’t always the same thing. That wound from the great battle might really have been obtained from falling off his dad’s horse when he was 5. Even more interesting from the point of a reader are the mysterious scars – the ones your point of view character notices and wonders about but doesn’t ask about.
Scars can form anytime there’s a break in the skin – from a paper cut to major damage. For the first 4-6 weeks after the injury, the scar will probably appear red and raised. The scar can then turn a sort of bluish-purple color, particularly if the scar is on a body surface that is prone to decreased blood flow or that is over a joint or flexible area of the body (like the knee). It can take up to a year (sometimes longer, depending on the individual) for a scar to look “old” or have its final appearance. Most old scars are white-silver and either flat or containing keloids.
Keloids are abnormal “lumps” that form during scar formation and are more likely to form on people of African descent or with dark skin tone. Keloids can grow massively large, taking over entire structures of the body and rendering them useless, particularly if formed on the hands, feet, or ears. Keloids can be painful, itchy, and continue to grow for months or years. Unlike normal scars, keloids do not get smaller or lighter with age.
Diseases like measles, chicken pox, and smallpox can leave survivors covered in patchy, white scars. Leprosy, despite being curable with modern treatment, can be horribly disfiguring to individuals who do not have access to treatment, culminating in gangrene and loss of limbs, blindness, and more. In a pre-modern society that is often struck by diseases and plagues, at least some of the people your characters interact with (if not your characters themselves) will likely show evidence of those same diseases.
Another type of scar to consider are the scars left on your society by plagues and diseases. Particularly in a world that lacks modern medical practices, plagues and diseases can cut a swath through a culture, changing the behaviors of the people within it.
Military camps were also prone to certain outbreaks and soldiers more often suffered and died from bacteria than from the enemy’s weapons. Typhus, particularly decimated more than one army in the field. Typhus is a disease that struck armies because hygiene was often poor. The deadlier form is more common in cold weather and is caused by a bacteria called Rickettsia typhi. It causes headaches, joint pain, light sensitivity, high fever, rash, cough, delirium, and stupor. Without modern treatment, 10-60% of those infected with typhus died, and the disease spread like wildfire through close camps, including armies, crowded transport ships, and jails. It was historically called “gaol fever” because of its rapid spread through prisons.
Cultural practices and superstitions may spring up around particularly deadly plagues. Songs and legends may develop, not unlike the children’s songs that are thought to be about the Black Death. Historically the special treatment and blessing of food in religious rituals was part observance and part an attempt to ward off illness. Common superstitions, religious practices, and unconscious cultural behaviors often arise as a response to disease events.
Cultures may also react strongly to anyone who shows signs of illness. Historically, lepers have been ostracized or even killed, along with their families. Those afflicted with leprosy were considered cursed, and superstition played a large role in the cultural treatment of these individuals. Leper colonies were common during the Middle Ages in Europe and India. Slave ships carrying “cargo” known to be ill with plague-like symptoms have been sunk rather than allowing their passengers to infect the port towns on the other side, and the corpses of infected people have even been catapulted over the walls of besieged towns as a primitive form of germ warfare.
Diseases have shaped the face of our world. They can add a lot of depth if you remember them when shaping yours.