Topical treatments, such as gels and emollients, are well-known treatments for psoriasis, a condition which causes red, scaly patches and inflammation. However, this may not be suitable for those with a more severe condition, this is where phototherapy comes in. Phototherapy utilises different wavelengths of light to help reduce inflammation and the overproduction of skin which causes psoriasis. Shedding light on potential benefits and limitations, this article delves into the use of UV light therapy as a viable option for managing symptoms of psoriasis. 

Introduction 

What is psoriasis?

Psoriasis is a chronic skin condition characterised by red, itchy, and scaly patches on the skin. It is most often seen on the trunk, outside of joints (distinguishing it from eczema), and the scalp - though it can appear on any part of the body.¹ It affects around 3% of the world’s population,² yet there is still no way to cure the condition completely.

It can be caused by a genetic mutation, meaning it can be passed down from family members, and occurs when new skin cells are formed much faster than they should be. This causes overproduction of skin cells, leading them to build up on the skin surface, which leads to the formation of the thick scales associated with psoriasis. This formation is mediated by a specific immune cell, called T lymphocytes, meaning it is characterised as an autoimmune disorder.¹

Current treatment options

There are many treatment options for individuals dealing with psoriasis, with the first line of treatment being topical gels or creams applied directly to the skin. This is particularly useful in mild cases or for use in combination with other treatments for more severe disease. 

Studies have shown poor adherence rates with topical treatments, with up to 60%³ of patients admitting to failing to keep up with application. This can be the result of many reasons, such as application times, a dislike of the associated smell/skin discolouration caused by the treatments, and a lack of immediate results. This creates a limitation in the possible positive outcomes, as topical treatments must be used consistently to have the desired effect.³

Phototherapy

Phototherapy harnesses the effects of UV waves to reduce inflammation and decrease the rate at which new skin cells are produced.⁴ This can both reduce the appearance of psoriasis scales and greatly increase the patient’s quality of life. Phototherapy has been used to treat many skin conditions and has been used for centuries by many countries to help with this. 

There are two main types of phototherapy used to treat psoriasis:

• Narrow-band UVB (NB-UVB)
• PUVA

Each treatment has its benefits and limitations and should be carefully discussed with a doctor experienced in UV light therapy before using it for psoriasis.

UVB therapy 

There are two types of UVB therapy:

• Broadband - uses wavelengths at 280-320 nanometres
• Narrow-band - uses wavelengths at 311-313 nanometres

In the 1970s, it was discovered that narrow-band UVB therapy (NB-UVB) significantly reduced the risks of burning associated with phototherapy and is now the first-line option for phototherapy in psoriasis patients. Broadband is still used occasionally in individuals whose condition does not respond to NB-UVB.⁵

How does the treatment work?

Significant improvement usually requires treatment around 3 times a week, totalling up to 36 sessions, with at least 24 hours between sessions to allow the skin to recover. Once this period is up, treatments can steadily be reduced to once a week to maintain the results on a long-term basis. Follow-up appointments should occur every 3 months for the first year, and then every 6 months afterwards to check the skin and the efficacy of the treatment.  

Unaffected skin should be protected to minimise UV exposure to the areas which don’t need it, including the eyes, where goggles can be worn, and the face and genitals, which can be wrapped with a towel. SPF 50+ sunscreen can also help protect unaffected areas. 

Skin must be free from any lotions or perfumes, and during treatment, only mild soaps should be used to reduce irritation to the skin. As well as this, water used for bathing should be warm at most, as hot water can also exacerbate irritation.  

Advantages

Total clearance using UVB treatment has been reported in around 60-70% of cases following the initial phase of treatment,⁵ showing this to be an effective method of managing psoriasis.

This treatment is also much less harsh than PUVA light therapy and is safe to use during pregnancy.

Possible side effects and limitations⁵

The main side effects of UVB therapy include: 

• Burning – this is rare and should be treated with topical steroids to reduce the severity 
• Photoaging – this includes wrinkling, increased skin fragility, and coarse skin 
• Tanning 

An increased risk of skin cancer is not associated with UVB therapy, particularly NB-UBV, as it uses a relatively safe level of UV to treat.  

PUVA therapy

UVA therapy, also known as photochemotherapy, uses UVA phototherapy in combination with a medication called psoralen, which helps prepare the skin to respond better to light waves. Psoralen comes in many different forms and can be taken as a tablet, applied topically as a gel or cream, or added to a bath solution in preparation for the procedure.⁴
PUVA uses higher wavelengths than UVB therapy, at 320-400 nanometres, which makes it more potent but this causes more risk of serious side effects. This is used as a second option after treatment has already been attempted with UVB and topical therapies, as it has a higher risk of long-term damage. 

How the treatment works⁶

There are two phases to PUVA therapy:

• Initial clearing

This involves a more intense regimen, with treatments occurring 2-3 times a week, totalling around 30 treatments which can take up to 15 weeks. 48 hours must be left in between each treatment to allow the skin to recover and reduce the risk of long-term damage. 

• Maintenance 

Once the treatment has cleared 95% of the visible psoriasis, the treatments can steadily be decreased to just once a month. From here, it can be discontinued if the patient is stable in remission and can be restarted if there is a flare-up. 

Advantages 

It is estimated that up to 90% of people treated with PUVA have noticeably improved symptoms or a complete lack of symptoms after treatment.⁴ This shows that this treatment is incredibly effective in the treatment of psoriasis. It also does not affect the immune system, so could be a more appropriate option for individuals who are immunocompromised or on medication which can suppress the immune system.

Possible side effects and limitations

Short-term side effects 

• Burning 
• Itching 
• Pigmentation 
• Nausea when psoralen is taken in tablet form 
• Tanning  

Long-term side effects  

• Cataracts (limited evidence shows this, however, it has been seen in animals exposed to UVA) 
• Skin ageing  
• Increased risk of skin cancer 

The main limitation of PUVA therapy is the increased risk of skin cancer. Since this therapy uses higher wavelengths, it causes more damage to the skin. This risk is higher in people with fair skin or who have previously been diagnosed with skin cancer.⁴ It is particularly important with this treatment to avoid further exposure to sunlight and to protect yourself while outdoors to prevent increasing this risk.  

Comparison of treatment options

There are many reasons an individual would choose one type of phototherapy over another, and it is important to discuss all the options with a qualified doctor, who can help with the decision. It is important to consider the risks and possible side effects as well as the efficacy when concluding. 

It is currently thought that PUVA therapy using tablets is the most effective option, however, it does carry greater risks than others. It is also more suitable for those dealing with immunosuppression. PUVA using a topical or solute form of psoralen is slightly less effective than the tablet form, though is still more effective than UVB alone. UVB can be made more effective when used in combination with the salt solution of topical treatments, although is still not as effective as any form of PUVA therapy. However, UVB is considered safer due to the lack of risk of skin cancer associated with this form of treatment, though there is a lack of studies affirming this. 

As well as this, higher doses and longer treatment regimens can also increase the risk of skin cancer. Individuals should not undergo more than 150 PUVA treatments using tablets in their lifetime to mitigate this risk, so other treatments may help reduce exposure.  

Summary 

• There are many treatment options available for those suffering from psoriasis, from topical creams to phototherapy. 
• Phototherapy is often used as a second option when topical treatments are not effective. They tend to show better results but have increased side effects. 
• PUVA therapy uses higher wavelengths than UVB and is therefore more effective but carries a greater risk of skin damage and cancer in the long-term. 
• It is important to discuss any considerations about phototherapy with a dermatologist who is experienced in this type of treatment, as the suitability of this will vary between individuals.