UV light therapy is generally safe when supervised by a dermatologist, but it does carry real risks that increase with the number of treatments you receive. The most common side effect is skin redness, occurring in roughly 9% of treatment sessions, while the more serious concern is a measurable increase in skin cancer risk with long-term use. How dangerous it is depends on the type of UV therapy, how many sessions you undergo, and whether you take certain medications.
Types of UV Therapy and How They Differ
The two main forms of UV light therapy used for skin conditions like psoriasis, eczema, and vitiligo are narrowband UVB and PUVA. They work differently and carry different levels of risk.
Narrowband UVB is the more commonly prescribed option today. It uses a specific wavelength of ultraviolet B light and causes skin redness that peaks 12 to 24 hours after a session. It’s considered safe enough for use in children and during pregnancy, and long-term studies have not found a clearly elevated skin cancer risk compared to the general population when treatment courses are kept reasonable.
PUVA combines ultraviolet A light with a light-sensitizing drug called psoralen, taken orally or applied to the skin before treatment. This combination is more powerful but also more dangerous. The skin reaction from PUVA peaks much later, around 96 hours after exposure, and patients need to protect their skin and eyes for 24 hours after taking the medication. PUVA is typically reserved for cases where narrowband UVB hasn’t worked or when someone has a severe form of psoriasis.
Common Short-Term Side Effects
A large observational study tracking over 1,200 patients found that about 19% experienced some kind of acute side effect during their treatment course. The most frequent issues were:
- Skin redness (erythema): 8.8% of patients
- Itching with redness: 1.9%
- UV burns: 1.4%
- Itching alone: 1.3%
These numbers mean the majority of people tolerate treatment without problems in any given session. UV burns, while uncommon, can involve second-degree damage to the upper layers of skin. Most side effects resolve on their own or with a temporary pause in treatment. Your provider will typically start with a low dose and increase gradually to find the right level for your skin type, which is the main strategy for avoiding burns.
Skin Cancer Risk With Long-Term Use
This is the concern that matters most, and the answer depends heavily on which type of therapy you’re receiving and how many sessions you accumulate over your lifetime.
A multi-center registry study of nearly 4,800 narrowband UVB patients found elevated rates of all three major skin cancers compared to the general population. The incidence of basal cell carcinoma was 2.5 times higher than expected, squamous cell carcinoma was 3.7 times higher, and melanoma was 4 times higher. Looking specifically at patients who had been followed for five or more years after their first treatment, the basal cell carcinoma rate remained elevated at 3 times the expected rate and squamous cell carcinoma at 3.8 times. Melanoma risk, however, dropped to only 1.2 times the expected rate at the five-year mark, a figure that was no longer statistically significant.
These numbers sound alarming, but context matters. Skin cancer rates in the general population are the baseline for comparison, and people receiving phototherapy already have chronic skin conditions that may independently affect their cancer risk. Still, the data makes a clear case for limiting the total number of sessions whenever possible.
PUVA carries substantially higher long-term risks. A landmark prospective study following 892 men for over 12 years found that the rate of invasive squamous cell carcinoma of the genitals was nearly 96 times higher than in the general population. Among patients who received the highest cumulative PUVA doses, that figure jumped to 286 times the expected rate. This is why dermatologists track lifetime PUVA exposure carefully and avoid using it as ongoing maintenance therapy.
Medications That Increase the Danger
Certain common medications make your skin significantly more sensitive to UV light, which can turn a standard phototherapy dose into one that causes burns or other reactions. The FDA identifies several categories of drugs that interact with UV exposure:
- Antibiotics: doxycycline, tetracycline, ciprofloxacin, and levofloxacin
- Diuretics (water pills): hydrochlorothiazide, furosemide, and chlorthalidone
- Pain relievers: ibuprofen, naproxen, and celecoxib
If you take any of these regularly, your dermatologist needs to know before starting phototherapy. In some cases the dose will be adjusted, and in others a different treatment approach may be safer. Even over-the-counter ibuprofen can be enough to alter your skin’s UV sensitivity.
Eye Protection Is Non-Negotiable
UV light can damage the lens and retina, so eye protection during every session is essential. Clinical guidelines require UVB-filtering goggles during treatment. The one exception is when you have skin lesions around the eyes that need treatment. In that case, keeping your eyelids closed is considered sufficient, since research has shown UV light does not penetrate through closed eyelids.
For PUVA patients, the protection window extends well beyond the treatment booth. Because psoralen circulates in your system and sensitizes your eyes to UV damage, you need to wear UV-blocking sunglasses for 24 hours after taking the medication, including indoors near windows.
Home Devices vs. Clinical Treatment
Home phototherapy units are increasingly available, and the question of whether they’re less safe than in-clinic treatment is reasonable. Research comparing home and clinical phototherapy, primarily in the context of neonatal jaundice treatment, has found that complication rates are similar between the two settings. The concern with home use isn’t that the devices are inherently more dangerous. It’s that without professional oversight, there’s a greater chance of errors like incorrect dosing, skipping eye protection, or failing to notice early signs of overexposure.
Home devices prescribed by a dermatologist typically come with a specific dosing protocol tailored to your skin type. Following that protocol closely is what keeps the risk comparable to in-office treatment. The main practical difference is that clinical settings allow your provider to examine your skin regularly and adjust doses in real time, which becomes more important as you accumulate sessions.
How Providers Minimize the Risks
The single most important safety measure is limiting total lifetime exposure. For PUVA, dermatologists track the cumulative number of sessions and avoid open-ended maintenance regimens. For narrowband UVB, the approach is similar: use the fewest sessions needed to achieve clearance, then transition to other treatments if possible.
Other standard precautions include shielding areas that don’t need treatment (particularly the face and genitals), starting with low doses and increasing incrementally, and scheduling regular skin cancer screenings for patients with high cumulative exposure. Men receiving PUVA are specifically advised to shield the genital area during every session, given the dramatically elevated cancer risk found in long-term studies.
For most people with moderate skin conditions, a course of narrowband UVB phototherapy involves 20 to 30 sessions over two to three months. At that level of exposure, the absolute risk of serious complications remains low. The danger increases meaningfully when treatment extends over years or when patients cycle through multiple courses without adequate monitoring.