Psoriasis is a chronic autoimmune condition characterized by the rapid buildup of skin cells, leading to thick, scaly, and inflamed patches on the skin’s surface. This accelerated skin cell turnover is driven by an overactive immune response from T-cells. Symptoms often improve during sunnier months, leading to questions about whether general sun exposure can be used as a treatment. Scientific evidence confirms that specific forms of ultraviolet (UV) light can indeed be therapeutic for psoriasis, though the type of light and the method of delivery are paramount.
How Ultraviolet Light Affects Psoriasis
The therapeutic effect of light on psoriatic plaques is primarily achieved through the ultraviolet B (UVB) spectrum, which is naturally present in sunlight. UV exposure works by targeting the underlying biological processes that cause the skin lesions. Specifically, UVB light penetrates the skin to suppress the function of the hyperactive T-cells that drive the inflammatory response in psoriasis.
This suppression is achieved when the UV light induces apoptosis, or programmed cell death, in the pathogenic T-cells and the rapidly dividing keratinocytes (skin cells). By eliminating these overactive immune and skin cells, the treatment effectively slows down the accelerated cell growth cycle characteristic of the condition. UV light also down-regulates the production of pro-inflammatory cytokines, such as IL-17 and IL-23, which are key chemical messengers in the psoriatic pathway.
The UV spectrum is divided into UVA and UVB, but UVB is the wavelength most effective for treatment. Narrowband UVB (NB-UVB), which concentrates the light around 311 nanometers, has become the standard. NB-UVB is preferred over older Broad-band UVB because it targets the therapeutic effect with greater precision. This focused approach allows the light to penetrate deeply enough to affect the immune cells without causing excessive damage to the surrounding tissue.
The Difference Between Tanning and Medical Phototherapy
While the sun contains the beneficial UVB rays, recreational sun exposure or using a tanning bed is vastly different from controlled medical phototherapy. Medical light therapy, often called phototherapy, is a precise, doctor-supervised treatment that delivers a carefully measured dose of UV light. This treatment is typically administered using specialized equipment, such as a full-body light box or an excimer laser, which emit the specific therapeutic wavelength of NB-UVB.
A dermatologist determines the exact dose and duration of exposure based on the patient’s skin type, the severity of the psoriasis, and the minimum dose required to cause a mild pinkness (minimal erythemal dose). The treatment schedule is highly structured, often requiring two to three sessions per week for several weeks, ensuring consistent, escalating exposure to achieve clearing without burning the skin. This controlled dosimetry is what makes medical phototherapy an effective treatment.
In sharp contrast, commercial tanning beds are not designed to treat medical conditions and do not offer this level of precision or control. Tanning beds primarily emit ultraviolet A (UVA) light, with a much smaller, inconsistent amount of UVB. UVA alone is relatively ineffective for treating psoriasis unless combined with a sensitizing medication called psoralen, which is a treatment known as PUVA.
Using a tanning bed as a substitute for medical phototherapy exposes the skin to high, unregulated doses of UVA, offering little specific therapeutic benefit for psoriasis. The radiation output is uncontrolled and inconsistent, meaning the patient is at a significantly higher risk of sunburn. Sunburn can actually trigger a flare-up of psoriasis in previously unaffected skin, a phenomenon known as the Koebner response.
Safety Concerns and Dermatologist Recommendations
Uncontrolled exposure to UV light, whether from excessive sunbathing or tanning beds, carries significant health risks that outweigh any temporary symptomatic relief. The primary concern is an increased risk of skin cancer, including basal cell carcinoma, squamous cell carcinoma, and melanoma. Indoor tanning before the age of 35, for example, is associated with a 59% increased risk of melanoma.
Beyond cancer risk, unregulated UV exposure contributes to premature skin aging, causing wrinkles, loss of elasticity, and sunspots. Individuals using certain topical treatments for psoriasis, such as coal tar or tazarotene, or systemic immunosuppressant medications, may be more sensitive to light, increasing their risk of severe sunburn and phototoxicity. Burns from tanning beds can also directly worsen the psoriatic condition.
Dermatologists universally advise against using tanning beds or sunlamps as a form of self-treatment for psoriasis. Anyone considering light therapy should first consult a healthcare professional to determine if they are a suitable candidate and to receive a prescription for controlled phototherapy. When outdoors, it remains important to use sun protection on unaffected skin, as even small amounts of excessive sun damage can be detrimental to overall skin health.