Survivalists and outdoorsmen add iodine crystals to water, because iodine chemically purifies and disinfects untreated water. These crystals are used as a temporary measure, as iodine can be toxic in large quantities, especially for children.
Iodine is also used for fingerprinting. Law enforcement uses these crystals in a process called fuming. Blown gently across surfaces, these crystals reveal fingerprints. This process is effective for latent prints.
The pharmaceutical industry uses iodine crystals in several medications that benefit the thyroid. Strong iodine, which is iodine and potassium iodide, protects the thyroid gland before and after radiation treatments. Patients who are living in regions where there has been a nuclear accident take iodine, as it prevents thyroid cancer. It is also effective in the treatment of hyperthyroidism, which is an overactive thyroid gland.
Iodine is used to disinfect parts of the body before medical treatments or surgery. Iodine crystals can be used in the production of methamphetamine. According to the National Drug Intelligence Center, "The Comprehensive Methamphetamine Control Act of 1996 identifies iodine as a List II chemical." The federal government regulates the sale of iodine crystals; even though they have several legitimate uses, they can also be used for illicit purposes.