What Is Psoralen?

Psoralens are chemicals found in certain plants. These chemicals make the skin temporarily more sensitive to light. As a light-sensitive drug that absorbs longwave ultraviolet radiation (ultraviolet A, or UVA), psoralen is used with a type of light therapy called PUVA therapy.

PUVA therapy is used to treat many different skin conditions, including psoriasis, eczema, vitiligo, and skin problems related to lymphomas (cancer of the lymph system that fights infections). Psoralens can be taken orally or can be applied topically.

This article will cover what psoralen is, how it is used in PUVA, conditions PUVA treats, how the treatment is administered, and more.

Definition

Psoralens are chemicals that can be found in certain plants. They make the skin sensitive to longwave ultraviolet radiation. That effect is temporary.

PUVA, a type of photochemotherapy, is a combination treatment that starts with taking psoralen orally or applying it topically to the skin and then exposing the skin to artificial UVA light.

The psoralen works to boost the amount of UVA that the skin absorbs. Once the light energy is absorbed in the skin, the psoralen interacts with human DNA. That interaction decreases skin inflammation, which helps to clear up skin and improve skin pain, itching, and irritation.

Two types of psoralen molecules are considered medically useful: Oxsoralen (8-methoxypsoralen also noted as 8-MOP, methoxsalen) and 5-methoxypsoralen. The Food and Drug Administration (FDA) has not approved 5-methoxypsoralen for use in the United States.

Oxsoralen, can be applied topically or taken orally. The use of topical Oxsoralen is rare because of the increased risk for side effects, including sunburns.

Uses

Psoralen plus UVA therapy (PUVA) is useful for treating many different skin conditions, as well as conditions that cause skin symptoms. 

Psoriasis

Psoriasis is an inflammatory skin condition that causes skin cells to grow too fast. Skin cells pile up as red, itchy, scaly patches that can appear anywhere on the body, including the knees, elbows, trunk, and scalp.

PUVA treatment for psoriasis is considered a second-line therapy often prescribed to people for whom topical treatments of ultraviolet light B (UVB) haven’t worked.

Vitiligo 

Vitiligo is a condition in which white patches (skin lacking pigment) develop on the skin. The extent of skin involvement in vitiligo varies from person to person. Vitiligo can either cover smaller, localized areas or many body parts.

PUVA phototherapy was introduced in 1948 for the treatment of vitiligo, and it has been widely used since. Research has shown it to be a safe and successful treatment for vitiligo in adults who don’t benefit from other treatments.

Eczema

Eczema is a condition that causes the skin to be red and itchy. It is common in children but can affect anyone regardless of age. Eczema is a chronic condition that goes through periods of flare-ups (worsening of symptoms) and remission (few or no symptoms).

PUVA is sometimes used to treat severe cases of eczema. Your doctor may recommend PUVA when other treatments, including standard UVB phototherapy, haven’t helped. With eczema, PUVA can clear up skin by affecting and calming skin inflammation.

Alopecia Areata

Alopecia areata (AA) is an autoimmune disease that causes hair to fall out, often in clumps around the size and shape of a quarter. The hair loss is different for each person affected—some people lose hair in a few spots, while others lose a lot of hair.

PUVA is sometimes used when hair loss is severe and widespread. It is also used when other treatments have failed or cannot be used.

Cutaneous T Cell Lymphoma 

Cutaneous T cell lymphoma (CTCL) is a rare type of cancer that starts in the white blood cells (T lymphocytes, or T cells) that normally help the immune system fight germs, bacteria, and other foreign substances.

With CTCL, the T cells develop abnormalities that attack the skin. The condition causes redness, raised or scaly round patches, and skin tumors. There are different types of CTCL, and the most common of these is mycosis fungoides.

PUVA can penetrate larger and thicker lesions of CTCL. In treating CTCL, psoralen is given orally for 1.5–2 hours before exposure to UVA light. Treatments are usually needed two to three days per week until a maximum response is achieved. It may take several months to see a change in skin symptoms.

Polymorphic Light Eruption

Polymorphic light eruption (PLE) causes rashes from sun exposure in people who have developed sunlight sensitivity. The rash appears as red, tiny bumps, or raised patches of skin. These skin flare-ups often occur in spring and early summer, when exposure to sunlight increases. The rashes will recur after the first episode.

PUVA has been reported as a treatment option for severe PLE. It may be used in the most severe cases and is generally done while symptoms are active.

Systemic Sclerosis 

Systemic sclerosis is an autoimmune disease in which the immune system attacks healthy tissues and causes changes in the texture and appearance of skin. These changes are due to increased production of collagen (a protein that forms fibers in skin).

PUVA has been utilized as a treatment option for systemic (body-wide) and localized sclerosis. It has been considered in more severe cases or treatments that are not responding to conventional treatments. Research has shown it to be a potentially beneficial treatment for skin symptoms of the condition.

Administration

Psoralen methoxsalen is taken orally or administered topically. It is given about 45 minutes to an hour before UVA exposure. The amount of psoralen used (dosing) depends on the patient's weight.

Your treatment options depend on the facility where your treatment takes place. According to a 2016 report, three types of PUVA therapy are used in the United States. All three types are administered in outpatient settings, such as dermatology and specialized medical clinics and include:

• Systemic PUVA (methoxsalen taken orally)
• Hand and foot soak (methoxsalen dissolving in water for soaking the hands and feet)
• Bath PUVA (methoxsalen dissolved in bath water for whole body soaking)

Once the oral psoralen has taken effect or the appropriate time has passed for the solution to soak in, you will be seated in the PUVA treatment box that surrounds you. You will be given towels to protect sensitive areas during treatment.

A nurse will assist you with positioning skin areas to be treated. The treatment will be set at a specific dose set based on a calculated dose of light treatment. The initial dosage is generally within 0.5–6 Joules per square centimeter (J/cm²) and is increased by 0.5–2.5 J/cm².

After the treatment, your nurse will advise you to wash off any psoralen solution and provide assistance, if needed. There are no additional steps if you were given oral psoralen.

PUVA therapy for treating psoriasis is done over two phases—an initial clearing phase and a maintenance phase. During the clearing phase, treatments are done two to three times weekly, within at least a minimum of 48 hours between sessions to reduce side effects, especially the potential for burns.

Treatment timelines are usually based on the diagnosis, the severity of symptoms, and patient compliance with treatments. General timeline estimates for treatment of psoriasis are 25–30 visits or for nine to 15 weeks.

When skin is 95% clear, a person with psoriasis can be placed on a maintenance schedule, in which the dosing and schedule can be steadily decreased. Once a person achieves remission, they can discontinue PUVA treatments. Treatments can be restarted if skin symptoms return.

Timelines and treatment schedules for PUVA will vary based on the condition being treated.

Eligibility

People with chronic skin conditions are eligible for PUVA treatments. Treatment is recommended for conditions that are characterized by rapidly multiplying cells where PUVA can slow down or stop this process.

Healthcare providers typically don’t prescribe PUVA therapy to children or teens because of the risk of side effects. However, there has been some research that shows PUVA can be an effective and safe treatment option for skin conditions that have not responded to other treatments.

One 2020 report in the Spanish journal Actas Dermo-Sifiliográficas reported on a retrospective study of children and teens under age 17 and 122 randomly selected adults who received phototherapy treatment (both PUVA and UVB) between 2002 and 2017.

Response for both types of phototherapy was 35% in pediatric patients, which was similar to the response in the adult patients. Around 16% of the children had adverse effects—mainly mild erythema (skin redness). There was a higher treatment adherence for the children.

Preparation

Before treatment, limit your alcohol consumption to reduce the possibility of dehydration after treatment. You should also avoid sun exposure while treating with PUVA and on nontreatment days, as your skin will be more sun sensitive.

At the time of treatment, you will be asked to remove clothing in areas of skin being treated. Areas that won’t be treated will be covered and protected.

If you have not applied sunscreen at home, it will be applied at your appointment to protect the neck, face, and backs of your hands. You will also be given special goggles to protect your eyes from UVA light.

You should let your prescribing doctor and the PUVA treater know about all medications you are taking. Some medicines, including over-the-counter (OTC) drugs, can increase your risk of side effects.

Aftercare

Since PUVA can make the skin sun-sensitive, it is important to take extra care of your skin between and after PUVA sessions. Advice includes:

• Apply sunscreen to all areas of uncovered skin.
• Wear sunglasses when you are outdoors. You should also wear sunglasses under fluorescent lights on treatment days.
• Avoid sun exposure on treatment and non-treatment days.
• Wear long-sleeve shirts, long pants, hats, and other protective clothing outdoors and near windows on treatment and non-treatment days.
• Limit or avoid alcohol while treating with PUVA.
• Make sure you regularly follow up with your dermatologist during treatment and once treatment is over.

Outcomes and Recovery

PUVA can be a safe and effective treatment option for treating many different skin conditions, including psoriasis.  Studies on PUVA therapy have found it can reduce skin symptoms by up to 80%.

Topical PUVA therapy has reported to be an effective treatment option for treating alopecia areata. Some people with the condition who have used this therapy have seen significant hair regrowth with minimal side effects from treatment.

Research on PUVA for polymorphic light eruption shows complete or partial remission in up to 65% of people.

Research on PUVA for treating systemic sclerosis shows PUVA can improve skin symptoms of the condition. This is due to reducing inflammatory proteins that affect the skin and promote skin inflammation. PUVA can also reduce collagen production, which also can improve skin symptoms.

While PUVA can treat and manage symptoms of various skin conditions, it isn’t a cure for any condition. Following successful treatment, skin symptoms will be less severe, and skin will be clearer. You may also have fewer flare-ups from a condition causing skin lesions, rash, redness, itching, and irritation.

Warnings and Contraindications

There are known risks of PUVA therapy. And while all treatments for chronic skin conditions come risks, those linked to PUVA might be much more serious because psoralen makes skin extremely light sensitive.

Risks of PUVA therapy include:

• Burning: Erythema (skin redness) can cause a burn similar to a sunburn. This reaction often occurs 48–72 hours after a treatment session, and you might need to stop treatment until it clears up.
• Tanning: PUVA can lead to a tanned skin appearance. Skin can also burn easily because of this tan.
• Itching: Dry and itchy skin is common following PUVA treatments.
• Skin aging: Some people may experience premature skin aging. Long-term PUVA therapy can lead to wrinkling and skin discoloration.
  
• Nausea: Psoralen can cause nausea in some people, especially when taken orally.
• Eye damage: Eye sensitivity is common in people who take psoralen treatments. Wear protective sunglasses to avoid eye redness and soreness.
• Skin cancer: PUVA can increase the risk for skin cancer, including squamous cell carcinoma and melanoma. This side effect is rare, but if you have additional risk factors for skin cancer, you should discuss those with your dermatologist before starting PUVA therapy.

Summary

Psoralen combined with long-wave ultraviolet radiation (PUVA light therapy) is used to treat many different chronic skin conditions, including psoriasis. Psoralen can be taken orally or administered topically. It makes the skin more sensitive to UVA light, which allows deep penetration of light to the skin.

After the psoralen has time to take effect, exposure to UVA light is given using a UVA box that surrounds the patient. A clinician will administer the treatment using a specific amount of energy. A treatment session ends after the appropriate dosing and timing have been achieved.

UVA therapy with psoralen can be a safe and effective treatment for most adults, although doctors are cautious about prescribing it to children and teens.

Risks include burning and other skin side effects, nausea, and the increased risk for skin cancer. After treatment has been completed, you should have your skin checked regularly for skin damage and signs of skin cancer.

A Word From Verywell

Skin conditions like psoriasis, eczema, and vitiligo can have an impact on your quality of life. Talk to your healthcare professional about your options for treatment. It is important to understand potential side effects and risks.