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Photodynamic Therapy

  • A sun damage treatment that relies on a photosensitizing drug and particular kind of light
  • Used to treat sun damage and actinic keratoses, or precancerous skin growths
  • A patient may need multiple sessions for a thorough treatment
  • Involves Dermatologic Surgery and Medical Dermatology

Photodynamic Therapy


Sun damage can sometimes be undone. A technique called photodynamic therapy directs wavelengths of blue fluorescent light to activate a topical medicine applied to the skin. It selectively kills abnormal, potentially cancerous cells in specific areas. 

“It’s a very effective way to treat a broad area of sun damage,” says Sean Christensen, MD, PhD, a Yale Medicine dermatologist. Photodynamic therapy procedures can be performed in one visit, though some patients require more than one treatment. “There isn't any surgery involved—no needles, either,” Dr. Christensen says.

Listed among the best dermatologists in the country, Yale Medicine dermatologists receive thousands of referrals each year from dermatologists and physicians throughout Connecticut and beyond to care for patients. At Yale Medicine, we tailor treatment to your individual needs.

What conditions can be treated by photodynamic therapy?

Photodynamic therapy is approved by the FDA for the treatment of actinic keratoses (AK), which are precancerous skin growths caused by sun-damaged cells in the epidermis (the skin’s outermost layer). 

“We think of these as precursors to skin cancer,” says Dr. Christensen. “The risk of any one of them going on to become cancer is very low, but people usually have multiple actinic keratoses on places like the forehead, cheeks or bare scalp. If they have a dozen growths in a given area, then there is a significant risk of skin cancer in that area.” 

The growths, which are red, pink or flesh-colored and scaly or crusty, don't usually hurt or itch, but they can be bothersome to look at and feel, so patients often want them removed. Photodynamic therapy is more practical and effective than other treatments for AK (such as liquid nitrogen) when there are multiple lesions. 

Treating an affected region of the skin is called “field therapy,” Dr. Christensen says. “Instead of treating 20 individual spots with liquid nitrogen or excision,” he says, “which can both be quite painful and leave scars, field therapy allows us to get all the spots at once and also treat spots below the skin's surface that aren't yet visible to the naked eye.” 

How does photodynamic therapy work?

The procedure involves three steps. 

  • Application: First, the dermatologist applies aminolevulinic acid (ALA), a liquid photosensitizing agent, directly to the affected area of the skin. “We'll usually do one defined region of the skin—maybe both cheeks, or the forehead and nose, or the top of the head,” says Dr. Christensen.
  • Incubation: Abnormal cells in the skin biochemically convert ALA into a naturally occurring substance called protoporphyrin IX, which is extremely sensitive to light. Most people have a trace amount of this substance in their skin, but it doesn’t usually cause any problems, Dr. Christensen says. The dermatologist will determine how long the incubation period should be. The longer the wait, the stronger the effect. 

For a patient with a milder condition (for example, someone who has only a few AK spots and has never been treated before), Dr. Christensen may start with about 90 minutes of incubation. For more serious cases (for patients with more and thicker spots that may have failed other treatments, for example), the doctor may increase the incubation time to two to four hours. Very rarely, the doctor will apply the medication in the afternoon and ask the patient to return the next morning for treatment. 

  • Exposure: After the incubation period, the patient sits in front of a U-shaped blue fluorescent lamp, which curves partly around the head from ear to ear for 16 minutes. During light exposure, patients will feel tingling or a mild burning sensation, but that stops as soon as the light is turned off. If the sensation becomes too intense for the patient, the doctor can turn off the light for a few minutes before continuing (pausing the treatment like this won’t affect results, Dr. Christensen says). 

The protoporphyrin IX absorbs the energy from the blue light and then converts it into oxygen free radicals, which damage and kill the abnormal cells. This would obviously be a problem if healthy, normal cells were damaged, too. But because the medication is activated by abnormal, potentially cancerous cells, they are primarily the ones eliminated during treatment.

What does the skin look like after treatment?

The treated area of the skin is usually quite red and may appear to be flaking or peeling, as it would after a mild sunburn. The redness, and perhaps some of the flaking, can last for several days to a week or even two weeks. (After that, skin returns to normal.) 

The area will also be more sensitive to light, so Dr. Christensen tells patients that they shouldn’t let any sunlight or very bright indoor lights hit the treated area for 48 hours after the procedure. “After two days of keeping the area covered and protected from sunlight, you can go back to their normal activities—of course, using sunblock as needed for outdoor activity,” he says. Most patients tolerate the procedure very well, with only moderate downtime. 

What else should you know about photodynamic therapy?

Photodynamic therapy doesn't just treat the lesions that you can see. This field therapy can treat existing spots and the earliest spots of sun damage that haven’t yet been diagnosed as actinic keratosis. “There's even some evidence to show that photodynamic therapy can decrease the rate of skin cancer formation in patients that have a lot of sun damage and who are at a very high risk of skin cancer,” says Dr. Christensen.

While one session can treat multiple actinic keratoses on a specific area such as the face or the scalp. But if the problem is that AK is caused by years of sun exposure, the effects take a long time to manifest. If a patient has multiple lesions on her cheeks, for example, he or she will probably also have damage on other parts of her face, or even the same part, that just haven't surfaced yet but will over time.

“In my experience with patients who have a high degree of sun damage, they'll often need to come back to treat new lesions,” Dr. Christensen says. “Because their skin is so damaged, it can be a constant battle to keep new lesions from popping up. Photodynamic therapy can be an effective way to treat skin issues before they become a problem, and before they even appear.” He establishes a schedule with his patients that includes periodic maintenance treatments as needed. 

What are the risks of photodynamic therapy?

“PDT is a generally safe procedure,” says Dr. Christensen. Aside from redness and peeling, some patients will experience a more severe reaction that involves blisters or scabs, but this also will be transient. 

In addition, the blue light can be irritating to the eyes, and for that reason, you wear protective goggles during the light treatment. In some cases, the dermatologist will cover patients’ eyes with moist gauze—like during a spa treatment, Dr. Christensen says. 

What makes Yale Medicine's approach to photodynamic therapy unique?

Dermatologists at Yale Medicine take an individualized approach to every case. For example, says Dr. Christensen, a patient with skin cancer on his nose may want more elaborate surgical reconstruction to restore its natural appearance after surgery. But other patients—perhaps if they're older, or they're experiencing separate health issues—might not want to go through these additional operations and would prefer the least-invasive procedure that restores optimal function. “We'll take your preferences into account when deciding on treatment,” Dr. Christensen says.  

Yale Medicine receives thousands of referrals a year from other dermatologists, so we're prepared to deal with every case, including the normal to the never-been-seen-before. With treatments like photodynamic light therapy, we can help reverse some of the damage accumulated from time spent in the sun. 

“And should skin cancer be detected, you want to have a surgeon with enough experience to know what to do to help you,” Dr. Christensen says.