I would feel real good if this was a feature or a mod for this game. just to make it a tad bit more challenging. here are some things I thought of.
rashes: you can catch this illness by running into poison ivy or getting bit by mosqitos. red marks will appear on the character and will stop and scratch every once in a while taking away 5 points of health. you can put on clothing that will decrease the amount of points everytime you scratch. the way to cure it is to craft lotion by the science machine. you can make it with 4 spider glands, 2 flower petals, and 1 mosqito sack. if however you cannot cure it, you can wait 5 days for it to go away.
common cold: You can catch this illness by staying out in the rain or snow without any gear on. the character will sneeze every once in a while taking away 5 points of health. you could craft a handkerchief that'll bring your health back up to 12 points, or you could eat some honey that'll bring your health back up by 5 points. The way to cure it is by going to the crock pot and make cold medicine with honey and berries. if however you cannot cure it, you can wait 3 days for it to go away.
stomach bug: you can catch this by eatting raw meat or monster meat. the character will vomit every once in a while taking away 10 points of health. having stomach bug will also slow you down and make you lose your appitite. you can eat flower petals that can ease your stomach by 1 point. you can also carry a hot water bottle around with you to bring your speed back. the way to cure this is by going to the crock pot and make stomach medicine with 1 mushroom, 2 flower petals, and 1 ice. if however you cannot cure it, you can wait 2 days for it to go away.
Phantazmal flu: you can catch this by being touched by a ghost or eatting glommer's goop. this is nearly like a cold but little bit different. the character will projectile sneeze exctoplasm taking away 20 points of health and 10 points of sanity. you can also use the handkerchief but will only give you 6 points of health. this illness is fatel and should the treated as soon as possible. the way to cure it is to go to the crock pot and make wet goop. this will cause the player to vomit and cure the flu. you've only got 10 days before the illness kills you.
Craftable items
Handkerchief: you can craft this with 2 silk and 2 papyrus with the scince . you will need to wash it after you use it for the third time
thermometer: you can craft this with 1 cut stone and 1 red gem with the alchemy engine. 100 for a cold, 101 for stomach bug, and 103 for phantazmal flu.
lotion: you can craft this with 4 spider glands, 2 flower petals, and 1 mosqito sack with the science machine.
ice pack: you can craft this with 10 ice and 2 pig skin with an alchemy engine. has duribility. DO NOT WARE DURING WINTER!
hot water bottle: you can craft this with 2 mosqito sack and 5 ice with the alchemy engine. heat the water bottle over the fire and it'll warm up. has a line that'll tell you if it's getting cold.