Aquagenic urticaria or Water Allergy: You wouldn't think anyone could be allergic to the one substance necessary for survival — the one that makes up most of your body — but it can happen. It's not a real allergy in that it doesn't trigger a histamine response, but some people develop itchy hives after exposure to water. The actual cause remains unknown. The most common treatment is smoothing on a capsaicin ointment to relieve the pain and itching.

Cotard's Delusion or Walking Corpse Syndrome: This rare mental disorder makes people believe they're actually dead or missing body parts. People with this illness tend to avoid eating and bathing, since they don't think they have to. Doctors believe that this disorder stems from a dysfunction in the area of the brain that connects emotions with faces, so they have complete detachment when seeing human faces and bodies, including their own. The best treatment appears to be electroconvulsive therapy.

Hypertrichosis or Werewolf Syndrome: This disorder causes people to grow thick hair all over their bodies, including their faces. A variety of triggers can cause the disorder. One is a genetic mutation, and the other is a rare side effect of anti-balding treatments. The hair can be removed through waxing or electrolysis.

Elephantiasis: Carried by mosquitos, the parasite that causes this condition blocks lymph vessels and prevents them from draining, leading to extreme swelling of the lower limbs and, in some cases, the testicles. Medications to kill the parasite exist, but it's best to catch it early. There are also surgical procedures for the testicles, but not for the limbs.

Alien Hand Syndrome: It might make you think of that terrible Idle Hands movie where Seth Green has a bottle jammed in his skull, but having a rogue hand that acts independently of its owner's will is a sad reality for some. It's a rare side effect of brain injury or of the surgical severing of the corpus callosum. There's no treatment for it, but the erratic motions can be managed with constant activity.

Xeroderma pigmentosum or Vampire Syndrome: Some people are more sensitive to the sun and its UV rays than others, and about one in a million people can't handle any UV rays at all. They have to be completely shielded from the sun at all times or else they run the risk of severe sunburn or even breakdown of the skin. They can also develop skin cancers more easily. People normally have enzymes that correct UV damage, but a genetic mutation causes these to malfunction in people with xeroderma pigmentosum. This disorder is often linked to neurological disorders.

Epidermodysplasia verruciformis or Tree Man Syndrome: This rare condition makes it look like tree bark is growing out of someone's skin. The bark-like tissue is actually a series of warts brought on by a genetic mutation that causes the skin to become extremely susceptible to human papillomaviruses that aren't typically harmful. There are treatments available, but no cure.

Fibrodysplasia ossificans progressiva or Stone Man Syndrome: This progressive genetic disorder turns muscle and soft tissue to bone over time. As kids develop into adults, they have a gene that turns cartilage into bone, but when functioning properly, it also knows when to stop. Those with FOP don't have that ability, so bone just keeps developing throughout their bodies. It exists in about one in 2 million people and there's no cure. Trauma makes it worse, so surgically removing excess bone material just makes the body produce more.

Cold urticaria or Cold Allergy: Being cold isn't fun for anyone, but some people have an actual allergic reaction to it — a histamine reaction just like an allergy to peanuts. If it gets serious enough, swelling in the throat and tongue can be fatal. People with this allergy take antihistamines like they would for any other allergy.

Foreign Accent Syndrome: This happens when someone begins uncontrollably speaking in a foreign accent of a language they may not even know. Sometimes they'll even mix accents together. It's very rare, but it's typically caused by brain damage after a stroke or head injury. This type of injury normally affects the way a person moves their mouth and throat, which changes the sound of their words.