Board Certified Adult & Pediatric Dermatology - DermaSurgery - Fellowship Trained Mohs Surgery - Harvard Fellowship Trained Laser & Cosmetic Surgery - Skin Cancer - Complex Skin Conditions

Photodynamic Therapy

Photodynamic therapy (PDT) involves the use of a photosensitizing medication that when activated by a light source, will result in some type of reaction. In dermatology, patients will often know this as “Blue Light” treatment; however, that only refers to the light source and in fact there are many light sources that can be used for this treatment.

What exactly is Photodynamic Therapy in dermatology?

Photodynamic therapy at Skin Wellness Physicians involves the use of the medication known as Levulan® that is dispensed to the physician in a stick known as the Kerastick® prior to application on the patient. On the day of the treatment, when treating actinic keratoses, ‘pre-cancers’, the skin is wiped dry or degreased with alcohol and the Levulan® is applied using the Keratick®. Levulan® is a precursor (aminolevulinic acid) of a metabolite that we make in the body naturally (protoporphyrin IX). We normally produce this metabolite at very low levels in the skin, but there are certain diseases that make this metabolite at high levels and they therefore develop skin rashes in the sun. Interestingly, as a result of these skin reactions in sunlight, they do not develop skin cancers in the sun-exposed areas.

Once the medicine is applied, the patient is then instructed to either wait in the office or is permitted to leave the office for some time before being brought back by the clinical staff for light exposure. The length of time depends on the target of the treatment (i.e. actinic keratoses, skin cancers, acne, etc) and the light source (i.e. blue light, red light, intense-pulsed light). Once enough incubation has taken place where an expected level of the final metabolite has been built up in the skin, the patient is then exposed to the light source (usually red or blue light) for a pre-determined amount of time. The length of exposure time is usually dependent on the medical condition being treated and the light source being used.

Why have I been recommended Photodynamic Therapy?

There are several reasons that your physician may have recommended photodynamic therapy. The most common reason to be prescribed PDT is for the treatment of pre-cancers, otherwise known as Actinic Keratoses. Actinic keratoses, or keratosis in the singular form, are the premalignant lesions of squamous cell carcinomas, the second most common form of skin cancer. Squamous cell carcinomas often will start as a premalignant actinic keratosis and then transform into a malignant squamous cell carcinoma. While squamous cell carcinomas can form without having to go through the premalignant stage, by treating the skin affected with actinic keratoses, the theory is that you are treating the premalignant actinic keratoses and the skin that has yet to develop the clinical presentation of the actinic keratosis. This will be commonly conveyed to the patient as treating the lesions that we see and those that we do not see yet.

To read more about the use and details of PDT, please visit our page on Skin Cancer at:

What is the difference between blue light and red light?

This is simple: depth. Blue light only penetrates the skin about 0.5mm while red light penetrates about 2-3mm. So depending on the physician’s clinical evaluation, he or she may determine that 0.5mm is enough or feel that a deeper treatment would be beneficial.

In fact, the United States is the only country in the world where blue light is the leading light source. This has to do with clinical trials. The company that makes the medication performed clinical trials using blue light so that they could patent blue light medical devices. Since red light was already an established therapy, there was no patent to be had. If a clinical trial was performed using blue light, then only blue light would be approved by the FDA and therefore the patent would corner the market for the company. The United States was late to implement PDT in dermatology when compared to the rest of the world, and is the only country that primarily uses blue light as a result of the FDA-approval. While red light is the standard of care globally, it is considered off-label in the United States. Due to blue light’s poor penetration, it is not a very good treatment for skin cancer, those at high risk for occult skin cancers, or acne; therefore, red light is often chosen if your physician is considering one of these factors. If your physician feels your sun damage to be strictly superficial, blue light is an excellent option.

What can I expect during the treatment?

Exposure to the light source is usually uncomfortable and we provide a skin cooling system known as a Zimmer cooler. It is more or less a sophisticated medical device that is like a powerful air conditioner on a hose that the patient can use to cool the skin while undergoing the treatment. If you are having the treatment on the face, particularly around the mouth or nose, the physician will often prescribe you a prophylactic dose of an anti-viral medication to avoid stimulating any cold sore breakouts.

What can I expect after the treatment?

The treated skin after the treatment will often be bright pink or red. Some discomfort may be noted for up to 48 hours following the treatment. Some weeping, scaling, and slight scabbing may be noted depending on the severity of the sun damage. The worse the reaction is for the patient, usually the better the results. The worse the reaction, usually the worse the sun damaged skin was prior to treatment. As a result of improvement of the sun damaged skin following the treatment, subsequent treatments may be less intense. This phenomenon is usually seen at about the third treatment.

  • For acne patients: a severe white head or pustular response is usually noted following photodynamic therapy. This is a result of the sebaceous oil glands being very sensitive to the treatment, which are the main target for the photodynamic therapy when treating acne and a sign of successful treatment. This may also happen to adults who are prone to adult acne.
    The downtime for patients is usually 7-10 days. At about the 7-10 day mark, one can expect significant scaling to take place in the treatment area.

As long as there is no open skin, one can wear makeup starting at about 48 hours.

Do I have to stay out of the sun following the treatment?

It depends. If you are uncomfortable in the sun, then stay out. If you are not uncomfortable, then you may be in the sun, but we recommend using sunscreen. The reason for the sun sensitivity following therapy is that the medicine that has built up in the skin during the incubation period may not have been completely spent during the light exposure and therefore is reacting with the sunlight. While this may result in some discomfort when in the sun for the first few days after the treatment, it is not a bad thing, but in fact therapeutic. Regardless of this trailing therapeutic reaction in the sun following the in-office procedure, we still recommend the use of sunscreen. A sunscreen that patients often enjoy following photodynamic therapy is Elta MD UV Clear. This product contains niacinamide that helps with red sensitive skin which is often the case following PDT, and is an excellent zinc-based sunscreen for all other times as well.

How many treatments will I need?

Again, it depends on what we are treating. Actinic keratoses are usually treated 3 times for the best results and 8 weeks apart because of insurance reasons. We recommend that acne be treated about 6 times. We often treat skin cancers twice.

Is there any after care?

At Skin Wellness Physicians, we strongly believe in the use of dilute vinegar soaks. We recommend a mixture of 1tbsp of white vinegar mixed in 2 cups of water. A stock of this solution should be made and refrigerated. The cool application of vinegar compresses will often soothe and heal the skin. Furthermore, the application of ointment based emollients such as Vaseline or Aquaphor can be very soothing and again we recommend refrigerating these items so that when applied, it is found to be very soothing.

Recommend Supplies:

  • Store brand white vinegar
  • Aquaphor or Vaseline
  • Elta MD UV Clear sunscreen