A principal source of advice, support and information on psoriasis and psoriatic arthritis
A registered charity no: 1118192
A registered charity no: 1118192
Most people who have psoriasis find that the sun helps to improve their skin’s appearance. For some the change is dramatic, with red scaly patches almost disappearing altogether during summer months in a warm climate.
In order to help clear psoriasis sun exposure needs to be spread over time. A week on a sunny holiday may help but rarely completely clears psoriasis, and if the skin is exposed too soon for too long, sunburn can result. It is important to increase exposure to the sun gradually, to allow your skin to adapt to the sun without burning.
Because ultraviolet light is so effective for many with psoriasis, it is often used in various artificial forms by doctors. Ultraviolet (UV) phototherapy is a highly effective set of treatments for psoriasis given by hospital dermatology departments. UV phototherapy is used in one of two forms: UVB or PUVA. UVB (ultraviolet B) uses short-wave UVB light while PUVA (psoralen ltraviolet A) uses a plant-derived photosensitiser (psoralen) with longwave UVA light. If you need these treatments, your GP can refer you to a dermatologist who will discuss the most suitable treatment for your psoriasis, including phototherapy.
People with psoriasis often face a dilemma: they have heard that the sun is good for their condition, yet are loath to reveal any more of their skin than they absolutely have to. You aren’t alone if you never sunbathe or are one of those who wear polo necks, long sleeves and trousers or leggings even on the hottest summer days.
The energy in sunlight ranges in wavelength from about 2500nm (1nm is one millionth of a millimetre) down to 280nm. Visible light lies between about 400nm in the violet to 700nm in the deep red. Beyond 700nm is infrared, which is felt as heat. Infrared is strongly absorbed by water, so when clouds pass in front of the sun we immediately feel the reduction in warmth. Wavelengths shorter than 400nm are ultraviolet: our atmosphere protects us from wavelengths shorter than 280nm, so we are exposed to ultraviolet wavelengths from 280-400nm. This region of sunlight is arbitrarily split into long-wave ultraviolet A (UVA) from 315nm – 400nm, and short-wave ultraviolet B (UVB) from 280-315nm.
On its own, UVA is not effective in improving psoriasis, which is why psoralen is used to sensitise the skin. However, UVB is very effective at improving psoriasis, providing that the plaques are not too thick or reflective. So, sunlight can help psoriasis by virtue of the UVB wavelengths it contains. The UVB wavelengths in sunlight are also very effective at causing the production of vitamin D in the skin. Vitamin D is essential for bone and skin health, so if the diet is deficient in vitamin D, sunlight will provide what is needed, and this may improve some skin disorders, including psoriasis.
As with any source of UV, sunlight comes with some dangers. UVA wavelengths penetrate to the deeper layers of the skin and are largely responsible for the tanning effect of the sun. However, UVA can eventually cause damage to the skin, resulting in the typical signs of photo-ageing: wrinkles, broken veins, sagging skin and ‘age spots’. Meanwhile, UVB is largely responsible for sunburn. It is thought that episodes of severe sunburn, especially in young people, increase the risk of melanoma skin cancer in the future. Also, bad sunburn can cause psoriasis to start where the skin is burned. So, it is wise to gradually expose your skin to the sun in order to avoid sunburn. Excessive lifetime exposure to all wavelengths in sunlight can increase the risks of skin cancers, and this has been illustrated in the great increase in the numbers of skin cancers seen in recent decades since overseas holidays have been affordable and widely available. You are at the highest risk if you are fair and your skin does not tan easily.
How long can I expose my skin to the sun before burning?
This depends on many factors, including:
The strength of the sun
This can be assessed by the UV index, announced in summertime weather reports. The UV index is a number representing the strength of the sun, and ranges from 1 to 11+. 1-2 represents low UV, 3-5 moderate UV, 6-7 high UV, 8-10 very high UV and 11+ extreme UV. In the UK the UV index rarely goes above 6 or 7.
Your sun sensitivity
This is described by the skin phototype scale, which describes how the skin reacts to sun exposure. Phototype I individuals always burn and never tan; phototype II mostly burn and tan lightly; phototype III rarely burn and tan moderately; phototype IV almost never burn and tan deeply.
Which areas of skin are exposed
For example, upper back and shoulders are more sensitive to the sun than the lower legs.
How much exposure you have already had
For example, if you have a tan.
If you are taking any medication that makes you more sun sensitive
For example, some antibiotics and painkillers can increase sun sensitivity in some people.
whether you are using sun protection
For example a sunscreen.
Some very approximate guidance can be given on how long individuals can tolerate the sun before burning. Assuming moderate sun strength (in Plymouth, a typically sunny area of the UK, the average sun strength in May to August is UV index 6), and for previously unexposed and currently unprotected skin, then exposure times possible before onset of sunburn are approximately: phototype I 5-10 minutes; phototype II 10-20 minutes; phototype III 20-30 minutes; phototype IV 40 minutes. (Source: EU fabric sun protection factor Standard 801)
While the sun can be beneficial it can also be potentially dangerous if not treated with caution. The following tips may help:
Sunglasses adequate protection of the eyes is essential. Too much exposure to ultraviolet light can cause cataracts. Any sunglasses are suitable if they have the ‘UV400’ label and a CE mark.If you work or sunbathe in the sun regularly good quality sunglasses are essential. For those having artificial light therapy particular care is needed.
PUVA/phototherapy treatments – some of these treatments can cause light sensitivity. If you are having any of these treatments please consult your phototherapy service for expert advice on protecting your eyes. Other topical medications used in the treatment of psoriasis may also cause sensitivity to sunlight. Again, consult your phototherapy service regarding advice about the sun and remain cautious about your exposure to sun.
Food and dietary supplements – there are certain herbal preparations or supplements, such as St John’s wort, that can cause photosensitivity in people. If you are taking these supplements and are embarking on a course of phototherapy treatment or spending time in the sun, you should advise your phototherapy service of the supplements that you are taking, for further advice and guidance.
Sunlight and skin cancer there is much evidence to show that damage caused by sunlight can result in higher risks of skin cancer and premature ageing. Sunscreens, clothing, and applying good sense can reduce your exposure and damage to skin areas. As always, if you are worried about any mole or other lesion on your skin it is advisable to get it checked for peace of mind.
It should be noted that commercial tanning beds in salons usually output UVA light with some tubes also outputting very small amounts of UVB (4% or less). It is not advisable to use tanning beds because neither the type of tubes used (and thus the amount of UVB in the spectrum) nor the intensity (and thus the UV dose delivered in the exposure time ) are accurately known. So the risks of excessive UVA exposure may not be offset by any benefits of helping to clear psoriasis. The same arguments apply to home sunbeds bought over the internet. There is strong evidence that use of sunbeds increases the risk of skin cancers, including malignant melanoma. For those who start using sunbeds before the age of 35 years the relative risk of malignant melanoma almost doubles.
Sunbeds should never be used by these groups:
When travelling abroad please bear in mind that you may need extra protection due to extra hours of daylight, stronger UVA and UVB rays and climatic conditions. It is essential to bear this in mind when choosing adequate sunscreens, clothing, headwear etc.
Glossary of terms
|nm||Nanometre: one millionth of a millimetre,0.000000001 metre|
|UV||Ultraviolet: wavelengths of light shorter than 400nm, beyond the blue/violet end of thecolour spectrum|
|UVA||Ultraviolet A: Light with wavelengths from 315nm to 400nm, or long-wave UV.|
|UVB||Ultraviolet B: Light with wavelengths from 280nm to 315nm, or short-wave ultraviolet|
|PUVA||Psoralen plus UVA: phototherapy treatment where the skin is sensitised using psoralen before exposure to UVA light.|
|NB UVB||Narrowband UVB: phototherapy using special UVB lamps.|
|TL-01 UVB||The same as NB UVB; TL01 is the designation of the special UVB lamps produced by Philips, the Netherlands.|
This article is adapted from the Psoriasis and the Sun leaflet.
Always consult a doctor or your healthcare provider