What is Psoralen?

What is Psoralen?


If you have a chronic skin disease such as psoriasis, you may be wondering about psoralen, a type of drug used in light-based treatments. 


In this article, we will discuss what psoralen is, how it is used, common side effects, and treatment options.


What is Psoralen? 

Psoralen is a type of medicine derived from certain plants. These natural compounds are found in citrus fruits including lemons and limes, figs, parsley, celery, certain fungi, and spices including cloves and bergamot. Scientists believe that in the natural world, psoralens are a plant’s natural insecticide.

Therapeutic treatments that integrate psoralen have been around since 1200–2000 BC. Ancient Middle Eastern and Indian healers would apply a topical psoralen solution to the skin and instruct their patients to get sun exposure. 

However, they may not have understood at the time that excessive sun exposure could be harmful. Today, we understand that the sun emits invisible ultraviolet radiation.



How is Psoralen Used? 

Psoralen is used as a photosensitizing agent that temporarily makes the skin more sensitive to light, increasing the amount of light that is absorbed by the skin. Psoralens are particularly reactive when they are exposed to ultraviolet radiation from 320 to 400 nm.

Today, natural sun exposure is still a viable treatment for certain skin conditions, but artificial light sources are also used to control the wavelengths and exposure to target specific conditions while minimizing potential tissue damage. 

Certain wavelengths of light can kill cancer cells, and others can slow the overgrowth of skin cells. UVA light, for example, is effective as a treatment for psoriasis, but it must be used with caution since it can also accelerate skin aging and even cause skin cancer.

In some treatments, psoralen is taken internally. Psoralen can also be applied topically to target a small treatment area or used in a bath to cover the whole body. Light treatment is then sometimes done once the psoralen solution has activated, typically 1-2 hours afterward.



How Psoralen Works

The skin absorbs psoralen. As it absorbs into the cells, psoralen acts on two therapeutic pathways. 

The first pathway is through activating changes in the DNA to decrease inflammation and reduce skin pain, itching, redness, and irritation. 

The second pathway is through reactions with oxygen, which produce reactive oxygen species that can cause damage to certain cells, such as cancer cells.

Psoralen does not suppress the immune system.



What is Psoralen Used For? 

Psoralen plus ultraviolet (UV) light makes up photodynamic therapy or photochemotherapy, to treat a variety of conditions.

Psoralen is sometimes used in combination with PUVA phototherapy, which is essentially long-wave ultraviolet-A (UVA) radiation. This is used for the treatment of severe chronic skin diseases. 

PUVA therapy involves oral or topical application of a psoralen solution, followed by exposure to UVA radiation. Treatments usually occur 2–3 times a week for several months.

PUVA treatment manages symptoms, but it is not a cure for any skin condition. Ultraviolet light may also cause long-term skin damage, including skin cancer.


How Psoralen Treats Psoriasis

Psoriasis is an inflammatory skin disease characterized by overgrowth of skin cells. Dead skin cells remain on the skin surface as itchy, scaly patches. 

PUVA therapy has been shown to be as effective as using pharmaceuticals in 62% of psoriasis patients. PUVA therapy is often an effective treatment for patients whose psoriasis skin plaques don’t respond to topical treatments or to UVB therapy and for patients with darker skin tones.

A significant clearing of psoriasis skin plaques is often achieved within 6–12 weeks. However, once-weekly maintenance treatments may be necessary to prevent the recurrence of the disease. 

PUVA therapy is a successful treatment for plaque psoriasis, guttate psoriasis, and palmoplantar pustulosis, a type of psoriasis that is localized on the soles of the feet and the hands, where the skin is naturally thicker.


Psoralen and Vitiligo

Vitiligo is a condition where the skin develops white patches without pigment. 

The condition can be localized or widespread. PUVA therapy can be a moderately effective vitiligo treatment.  


Psoralen and Eczema

Eczema is a chronic inflammatory skin condition that causes redness and sometimes severe itching. It is most often seen in children but can appear in adult patients as well. 

PUVA therapy can be used to treat severe eczema when UVB phototherapy or other treatments haven’t worked.


Polymorphic Light Eruption

Polymorphic Light Eruption (PLE) is a condition where rashes appear on the skin of sun-sensitive people after sun exposure. These occur most often in spring or summer, may cover the whole body, and will recur.

PUVA treatments are most effective in severe PLE cases.


Systemic Sclerosis

Sclerosis is an autoimmune disease that results in the overproduction of collagen, causing hardening and thickening of the skin. 

PUVA therapy can treat severe localized and systemic sclerosis that doesn’t respond to conventional treatments.


Psoralen and Cancer Treatment

Psoralen has also been used in PUVA photochemotherapy to treat certain cancers including cutaneous T-cell lymphoma (CTCL). This rare type of cancer originates in the white blood cells called T cells, which are part of the immune system. 

In CTCL, the T cells develop abnormalities that cause them to attack healthy skin cells, causing redness, tumors, and raised/scaly round patches.

PUVA treatment has the ability to penetrate deep into skin lesions, and skin symptoms start to ease up after several months of treatment.


Alopecia Areata

Psoralen can be used to treat alopecia areata (AA), an autoimmune disease that causes severe hair loss. PUVA treatment can be used on localized hair loss or the entire scalp.



Drawbacks to Psoralen

In humans, large amounts of psoralen create a phototoxic reaction that manifests as pigmentation, blistering, and redness. 

However, since it is rare for people to have more than a small amount of psoralen in their regular diet, they are generally well-tolerated when administered therapeutically.

Psoralens are effective at treating chronic skin conditions but can have side effects.

Oral psoralen use may cause nausea. The patient may feel burning, skin redness, and itching after treatment. Long-term use can lead to premature skin aging.


When the skin absorbs psoralens, the skin becomes more sun-sensitive with an increased risk of sunburns and skin cancers, including squamous cell carcinoma and melanoma.

Psoralens can also cause a tanned appearance. However, they accelerate skin aging, so these compounds are not recommended as natural tanning aids. The result over the long term would be skin increasingly damaged skin.

Other than skin problems related to PUVA treatments, oral psoralen use has been linked to eye sensitivity, eye redness, and even cataracts. 

Psoralens should not be used if you’re pregnant or breastfeeding, or if you are taking certain drugs.


There is some evidence that psoralen treatment is poorly tolerated by those with liver disease. It is believed that psoralens cause liver damage, but these effects have been most notable in patients with existing liver disease.

Possible side effects of oral psoralens include nausea and vomiting, skin rashes, and itchy skin. 

The patient will be instructed by their doctor to avoid certain foods during photodynamic therapy or photochemotherapy. These foods include the natural psoralen sources as well as carrots and parsnips. Extra psoralens found in certain plants boost the skin’s sun sensitivity even more, which can lead to sunburns.  

And since a psoralen solution is most often used with ultraviolet light, it automatically increases the risk of skin damage.



Psoralen Alternatives

Given that PUVA treatments can cause unwanted side effects, are there any alternatives? Yes. And, many of these treatments can be administered at home, with a physician’s guidance: this is great news if you are a psoriasis patient.


Red Light Therapy and Psoralen

Red light therapy is a type of light treatment that delivers red and/or near-infrared light treatment. This is administered via light-emitting diode (LED) devices, to treat a variety of skin problems and other physical ailments.

In a clinical setting, red light treatment can be combined with psoralen. It is then called photodynamic therapy, which is sometimes used in the treatment of vitiligo and psoriasis. 

Treating psoriasis using RLT is different from PUVA photochemotherapy in that red light treatments do not contain long-wave UVA light, making it a great alternative for patients with sensitive skin.

In the case of skin cancer treatment, red light is administered by a doctor along with photosensitizing drugs to create a phototoxic effect that kills cancer cells. This has been shown effective in the treatment of cancer in the esophagus, lungs, and the skin and doesn't increase the risk of skin damage that UV light treatment can.


Red Light Therapy Usage without Psoralen

However, red light therapy alone (without the use of psoralen) can treat signs of aging including sun damage, age spots, fine lines and wrinkles, rosacea, and skin wounds. 

The treatment can be done in the convenience of one’s home using RLT panels. These are high-powered medical-grade LED devices such as the BIOMAX series that deliver superior light energy to the skin without any UV light.

The effect of red light on psoriasis and other skin diseases has been well-documented. The treatment doesn’t come with the adverse effects of UV light treatments. If you’re taking photosensitizing drugs including psoralens, we recommend talking to your doctor before starting RLT treatment at home. Otherwise, red light therapy treatment alone does not require a prescription and has few to no side effects. 

The BIOMAX series LED devices are incredibly versatile and feature therapeutic red, near- infrared, and blue wavelengths. 

You can treat a wide variety of physical conditions including sore muscles, hair lossarthritis joint painlow back painneuropathy, and more as well as most skin conditions. 

Learn more by browsing the Learning Center, which has tons more information about red light therapy and the various treatment benefits of red light therapy. 


Back to blog