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Psoralens are molecules found naturally in plants like turnips, celery, figs, and parsley. Since the 1970s, synthetic versions of these molecules have been available for use in medical treatment and research. These molecules are highly UV absorbent and this trait can be harnessed in a variety of different ways. Their UV absorbency also makes them dangerous and it is important to handle isolated psoralens with care to limit the risk of injury.
In medicine, psoralens are sometimes used in the treatment of severe skin conditions like psoriasis, vitiligo, and eczema. If these conditions do not respond to other treatments, UV therapy can sometimes be beneficial for the patient. Applying psoralens before the treatment increases the skin's absorbency, heightening the effects of the treatment. The compounds may be made available through ingested pills or a bath soak the patient is directed to take before a treatment takes place. Treatments are conducted in booths or isolation chambers to allow for even and uniform exposure.
The risk with using these compounds in treatment is that the increased photosensitivity continues outside a doctor's clinic or office. If the patient is exposed to sun after a treatment, severe burns can result because the molecules will absorb UV radiation. Long term use of psoralen therapy can be dangerous for patients and may increase the risk of skin cancer. This is a risk patients must weigh when pursuing treatment for severe skin diseases. Taking care to avoid sun exposure can mitigate the risks, but will not entirely eliminate them.
Psoralens are also known to be mutagens. When they are present in DNA and UV exposure occurs, they can cause mutations in the DNA. This is potentially medically useful because the compounds could be used for activities like sterilizing; the psoralens will ensure that the UV radiation reaches all organic materials with DNA, like bacteria and viruses, killing them and cleaning the environment.
Plants developed psoralens as a form of natural pest control. These molecules are deadly to insects and when insects attempt to feed on plants that contain them, they will sicken and die. The amounts present in plants are not large enough to cause increased photosensitivity and DNA mutations in humans, making it perfectly safe to eat foods like celery and parsley. Commercially produced synthetic psoralens used in therapy and medical research are usually controlled to prevent people from accidentally coming into contact with them.