What Are Psoralens?

Medically Reviewed by Debra Jaliman, MD on March 12, 2024
4 min read

Psoralens are medicines made from plants. They make your skin more sensitive to light. Methoxsalen is the most common psoralen drug.

Today, doctors use psoralens with sunlamps or light booths that emit ultraviolet light. This is called PUVA or photochemotherapy.

Psoralens usually come in capsules that you swallow. You can also soak your body in bathwater with a psoralen solution. If you just need to treat a small area of skin, like one hand or foot, you can soak that part in psoralen solution or rub on psoralen lotion or gel.

Psoralens boost the amount of ultraviolet light your skin absorbs. This lets the light into your skin. The ultraviolet radiation helps treat severe skin diseases like psoriasis, vitiligo, polymorphic light eruption, and cutaneous T-cell lymphoma, a type of cancer.

Ultraviolet light can slow down the overgrowth of skin cells that form psoriasis plaques, or rashes. In the 1970s, doctors found that psoralens and ultraviolet light together could clear up psoriasis skin plaques. It can also help treat vitiligo, which is a loss of pigment in the skin.

PUVA is about as effective as biologic drugs for psoriasis in 80% of people with this skin disease.

Psoralens are natural products found in plants such as limes and lemons, celery, bergamot, parsley, figs, and cloves.

Psoralens are an old and effective natural treatment for skin conditions. In ancient times, doctors gave people with skin problems herbs that were most likely psoralens, and then told them to expose their skin to sunlight.

Psoralens affect your DNA to stop cell growth in one of two ways. One group intercalates, or weaves itself into, DNA strands after your skin is exposed to ultraviolet light. This group includes 5-methoxypsoralen and 8-methoxypsoralen. The second group creates monoadducts, or links, to an individual base -- the cross-pieces inside a DNA strand.

You take psoralen capsules about an hour before a whole-body PUVA treatment.

After you remove the clothing over the treatment area, you step inside a cabinet fitted with UV bulbs. Treatments will start off short, about 1 to 10 minutes, and increase in length each time.

You’ll get PUVA treatments about two to three times a week for 12 to 15 weeks. After that, a once-a-week treatment should keep your skin clear.

During the treatment, you’ll wear goggles to protect your eyes (PUVA can cause cataracts) and cover your face and groin to prevent burns.

For localized PUVA, you can just soak the area in psoralen solution (you might hear it called bath PUVA) or rub on psoralen gel 30 minutes before UV light therapy. You’ll use a small device that points light at that area, not your whole body.

Psoralens can make your skin more sensitive to sunlight. They can raise your risk of sunburn, cataracts, and skin cancer. And your skin might age faster.

Don’t use psoralens as a way to get a quick suntan. You should use these only as directed by your doctor.

Other short-term side effects of oral psoralens include:

To ease nausea, take your psoralen with a glass of milk or a meal, or take ginger supplements. Rarely, oral psoralens can cause liver problems.

Don’t eat limes, carrots, celery, figs, parsley, or parsnips while you take oral psoralens. It could boost the amount of natural psoralen in your system and make your skin even more sensitive to the sun.

Psoralens and UV light therapy can help people with psoriasis who don’t get results from topical ointments or plain UV therapy.

If you have stable plaque psoriasis, guttate psoriasis, or psoriasis on your palms or soles, PUVA is more likely to work for you.

Unlike biologic drugs used to treat psoriasis, psoralens don’t suppress your immune system. They may be a better option.

Pregnant women shouldn’t take psoralens. Studies show they can harm your baby. There’s less information about psoralens and breastfeeding. You and your doctor can discuss using them if you’re nursing.

Don’t take psoralens if you’re also taking the drugs anagrelide or tegafur. You may be more likely to have side effects if you take psoralens along with the drugs phenytoin or fosphenytoin.