Casey Gallagher, MD, is board-certified in dermatology and works as a practicing dermatologist and clinical professor.

Phototherapy is a medical treatment in which natural or artificial light is used to improve a health condition. Treatment could involve fluorescent light bulbs, halogen lights, sunlight, or light emitting diodes (LEDs).

Phototherapy is also known as light therapy and heliotherapy. Which type of therapy you need and how the light is used can vary depending on if the phototherapy is for eczema, psoriasis, or other health conditions.

This article explains how light therapy is used to treat these conditions. It also discusses some of the risks involved.

Phototherapy has been used to treat medical conditions for over 3,500 years. In ancient India and Egypt, people used sunlight to treat skin conditions like vitiligo.

Modern phototherapy began with Niels Ryberg Finsen. He used sunlight and ultraviolet (UV) light to treat lupus vulgaris , a type of tuberculosis that affects the skin. Since then, phototherapy use has grown. Today, light therapy is widely accepted.

There are three main types of light therapy used for skin disorders:

Broadband UVB: Broadband UVB uses a wide range of UVB rays. UVB rays are present in sunlight, but you can't see them.

Narrowband UVB: This involves using a smaller, more intense part of UVB to treat the skin condition. It’s the most common type of light therapy used today.

PUVA: Psoralen ultraviolet-A, or PUVA, combines UVA light with a chemical called psoralen, which comes from plants. Psoralen can be applied to your skin or you can take it as a pill. It makes your skin more sensitive to the light. 

PUVA has more side effects than some other light therapies. It's only used when other options haven't worked.

Phototherapy can be used to treat many skin conditions, including:

Phototherapy treatment involves using ultraviolet (UV) light to slow skin cell growth and inflammation. Inflammation is one of the ways your immune system responds to infections, injuries, and foreign "invaders."

UVB rays affect the outermost layers of the skin. UVA rays are slightly less intense, but penetrate more deeply into the skin. These two types of UV light can be used in different ways.

The effects of light therapy for skin disorders are usually temporary. Phototherapy for skin conditions may take six to eight sessions and up to two months to work.

Phototherapy for skin conditions is generally considered safe. However, side effects include redness, dry or itchy skin, nausea (with PUVA), blisters, or folliculitis, an infection of the hair follicles. Long-term side effects include skin cancer and premature skin aging.

Light therapy is also used to treat mood and sleep disorders.

Seasonal affective disorder is a type of depression linked to certain seasons of the year. It usually begins in the fall and lasts through winter. Light therapy for SAD involves using a lightbox—a specially designed box that emits a steady, soft light.

Light therapy used this way has a number of side effects you should be aware of. They include:

Light therapy is seen as a good treatment option because the side effects usually aren't serious or permanent. It is also inexpensive compared to other therapies.

If you take an antidepressant, light therapy may make it possible to lower the amount of medication you use. However, talk to your healthcare provider first before changing your antidepressant dose. Stopping your antidepressant has some health risks.

Phototherapy has also been explored for other kinds of depression. Some studies support it, but not all health experts agree that light therapy helps with depression.

Your body has an inner "clock" that times your sleeping and waking cycles. It's known as your circadian rhythm, and it doesn't always work the way it should.

Light therapy can help those who have circadian rhythm sleep disorders such as delayed sleep phase syndrome (DSPS). People with DSPS often can't fall asleep until the wee hours of the morning or close to sunrise. Light therapy can help them shift to more normal sleeping times.

It's important to time the light therapy correctly. Your sleep specialist will help you plan the right time to use light based on your symptoms.

A type of light therapy known as photodynamic therapy is used to treat some kinds of cancer and precancers. It involves using a drug called a photosensitizer along with light.

Photosensitizers are applied to the skin. When light strikes the skin, it interacts with the drug to make a kind of oxygen that kills nearby cancer cells.

Photodynamic therapy is used to treat conditions such as:

Photodynamic therapy is sometimes called photoradiation therapy or photochemotherapy.

Phototherapy has some advantages over treatments like radiation and chemotherapy. For example, it doesn’t usually have any long-term side effects. It leaves less scarring than surgery. And phototherapy costs a lot less than the other treatment options for cancer.

The downside is that it usually only works in areas on or just under the skin, where light can reach. It also does not help much with cancers that have spread.

Light therapy has been used for over 60 years to treat hyperbilirubinemia and jaundice. These conditions cause a baby’s skin, eyes, and body tissues to turn yellow. The yellow color comes from too much bilirubin, a pigment made when red blood cells break down.

Light lowers the baby’s bilirubin levels.  It breaks down the bilirubin so the baby's body can get rid of it properly.

There are two main ways to treat jaundice with light therapy. The usual way is to place the baby under halogen spotlights or fluorescent lamps. The baby's eyes are covered during the phototherapy treatment to protect against damage to the retinas.

Another technique is to use "biliblankets." The blankets have fiber-optic cables that shine blue light onto the baby's body. This method is most often used when babies are born early or when other treatments have already been tried.

Compact fluorescent lights and blue LED devices are also used to give babies phototherapy. They can be kept close to the body because they do not produce a lot of heat.

Light therapy for treating hyperbilirubinemia and jaundice is considered very safe. People sometimes have short-term side effects such as diarrhea, rashes, overheating, and water loss or dehydration.

Light therapy carries some risks. Here's a brief list to consider:

UV rays can damage your skin cells. They can cause your skin to look and feel older more quickly. This premature aging of the skin is also known as photoaging.

Some older studies found that being exposed to high amounts of artificial UV light raised the risk of skin cancer. Newer studies have found that PUVA may increase skin cancer risks, while narrowband UVB treatment poses no extra skin cancer risk.

If you have light therapy often, it can suppress your immune system, leaving your body more open to diseases, infections, and skin cancers.

Having PUVA treatments for skin or photodynamic therapy for cancer can make your eyes more sensitive to light. Sensitivity can lead to eye damage if you are exposed to sunlight or other bright lights. Light therapy may also cause you to develop cataracts.

People with certain health conditions may need to avoid light therapy. If you fall into one of these categories, make sure your healthcare provider knows about your condition:

Light therapy can be used to treat skin conditions, mood disorders, sleep disorders, some cancers, and jaundice in babies. Some treatments involve exposure to natural or artificial light. Others combine light therapy with a drug that makes the light more effective.

While light therapy is considered safe, some people do have side effects. And it's not right for everyone. If you're pregnant or nursing, have a family history of skin cancer, or have liver disease or lupus, light therapy might not be helpful.

Phototherapy is a great option for treating many conditions. However, you should consult with your healthcare provider before you use phototherapy at home to ensure you're getting the most benefit with the least side effects.

This depends on what you're being treated for, how severe your case is, and how often you get phototherapy. With eczema, you may start to see it improve after a month or two of regular treatment.

Until their bilirubin levels are normal. This often takes less than 24 hours, but some babies may need the light exposure for up to a week.

Low-level laser therapy, a type of phototherapy, has been shown to promote hair growth for men and women who experience pattern hair loss.

There is a risk, but it’s a small one. Most studies don’t show an increased risk in patients who receive phototherapy. Taking steps to protect areas of the skin not being treated and avoiding extra sun exposure can lower your risk.

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