Dr Jennifer Crawley talks about light treatment for psoriasis

Psoriasis is treated with topical therapy (e.g. creams), light treatment and systemic drugs. In this blog post, Dr Jennifer Crawley explains how specific light treatment for psoriasis is different from just going out in the sun or moving to a sunnier clime.
Light Treatment PsoriasisJane: A friend of mine years ago emigrated to Australia because she had psoriasis. She was told she had to be in a climate that had more sun and yet at the same time we have got to advise patients with psoriasis to have sun protection. So what would be the overall advice?
Jennifer: So, we know Jane that light therapy or UV treatment can help psoriasis and that is why we use phototherapy as a treatment. In medicine, everything is a balance of risks and benefit, so while we use light therapy as a treatment for psoriasis, we use a specific part of the light spectrum, most commonly, UVB to treat psoriasis.
Jane: What does the sun emit?
Jennifer: So the spectrum of light has different parts to it and emits mostly UVA and some UVB. UVA has a longer wavelength and penetrates more deeply than UVB. It plays a role in photo-ageing and contributes to skin cancers. UVB is the leading cause of skin reddening and sunburn. It tends to damage the more superficial layers of the skin and plays a crucial role in skin cancers. It is essential that any light therapy is provided in a setting so doses can be given and monitored in a controlled way.
Jane: And is that done in a specialised laboratory in the hospital, the light therapy?
Jennifer: So the light therapy is done in the hospital setting, and you stand into a large cabin called the UVB machine or phototherapy machine, and the nurses giving you the light treatment will set the device to a certain level or dose of light. For example, some people with very fair skin will need a lower level of light. Some people with darker skin will tolerate higher wavelengths of light. It is critical that that is done by very specialist phototherapy nurses and indeed Jane before we treat with phototherapy it is essential that patients have a light test called a MED test on their skin.
Jane: MED?
Jennifer: Minimal erythema dose, this is defined as the amount of UV radiation that will produce minimal redness on an individual’s skin within a few hours following exposure. This test is done before initiating phototherapy treatment and allows us to know what exact wavelength of light to begin therapy. We start at a low wavelength of light and then we will very slowly increase this over time.
Jane: Which part of the body do you test it on?
Jennifer: So we normally test it on any part of the body that is not affected by psoriasis, quite often the best place is the back.