What is Photodynamic Therapy? - Toronto Dermatology Centre
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What is Photodynamic Therapy?

Photodynamic therapy (PDT) is used for the treatment of both actinic keratosis (pre-cancerous red rough skin lesions) and acne. It has also been known to treat rosacea. At Toronto Dermatology Centre, we offer two different forms of PDT: one where Levulan is the active medication applied to the skin and Metvix, a newer, stronger formula involving less sessions and during the warmer weather can be activated by natural sunlight.

The benefits of photodynamic therapy for actinic keratoses is that rather than only spot treating individual clinically evident lesions on an ongoing basis, PDT provides a “field treatment” to areas of the face for instance which have substantial “subclinical lesions” or lesions that are under the surface just waiting to come up. In this way, PDT is a much better proactive and preventative treatment, rather than just the typical reactive liquid nitrogen treatments (“bandaid solution”) that we perform once lesions have risen to the surface.


Photodynamic therapy involves three steps: a topical solution of aminolevulanic acid (ALA) also known as Levulan, is applied to the area to be treated, the solution is left on the skin for 60-90 minutes to incubate, and then a light or laser source is applied to the skin to activate the Levulan.

ALA occurs naturally in our bodies and so is easily absorbed into the skin. At Toronto Dermatology Centre, we use BBL (Broad Band Light) as our light source. Since ALA causes the skin to be extremely photo sensitive, the addition of BBL to the skin acts as a catalyst to activate the solution and releases singlet oxygen that targets active cells in acne or actinic keratosis. Surrounding normal cells receive minimal damage.

Photodynamic therapy is a non-invasive treatment with minimal downtime. It can involve 2-6 treatments depending on the severity of the condition. Treatments are usually performed 2-4 weeks apart, depending on what condition is being addressed. Maintenance treatments may be required.


Also known as methyl aminolevulinate, Metvix acts in a similar fashion to the Levulan form of PDT. However, Metvix penetrates deeper and results in more powerful improvement. It can be activated two ways:  with red light filtered BBL or by natural sunlight. Generally 1-2 sessions are prescribed, about a month apart, and yearly maintenance should be considered.

During the colder seasons Metvix is applied and allowed to incubate similar to Levulan, followed by BBL light. 

During warmer weather, the patient will have the option to use outdoor light as an activation tool, where they will be outdoors in indirect sunlight for about 2.5 to 3 hours before going indoors. At this point avoiding sunlight for 48 hours post activation is advised.

The benefits of photodynamic therapy with BBL not only addresses the immediate concern for the patient (acne, actinic keratosis), but also helps with sun damage, collagen stimulation, smoothing fine lines and wrinkles, reducing broken blood vessels and sun freckles, and improving the general overall tone and texture of the skin.

Who should not use Levulan/ Metvix:

Levulan / Metvix is not recommended for patients who have a skin photosensitivity such as lupus, porphyria or sun allergy. It is important to tell your doctor or skin care specialist if you are taking oral medications (e.g. accutane, soriatane, toctino, tetracycline, ciprofloxacin, lasix, NSAIDs, hydrochlorothiazide) or using topical prescription or non-prescription products. Levulan/ Metvix is not recommended for pregnant or nursing females.

What are the possible side effects? 

Most common side effects are: scaling/ crusting, temporary hypo/ hyper pigmentation, itching, stinging, redness and mild swelling. Peeling will most commonly occur about three days after treatment. Skin may feel dyhydrated and sensitive. At Toronto Dermatology Centre, we suggest products that will help you through the first few days of discomfort. 

What precautions should I take?

Avoid sun exposure for at least 48 hours after treatment. Avoidance is best, and hat/sunglasses are the next best option. A medical grade sunscreen or preferably sunblock should be worn during this time.

How do I know if this is the right treatment for me?

At Toronto Dermatology Centre, consultations are complimentary with one of our medically supervised skin care experts. If you have acne, rosacea, or have actinic keratoses, book a consultation to see if this is the right treatment for you. All your questions and concerns will be addressed, and any additional information can be obtained at that time.

 ~ Sheri Roselle, Medical Esthetician at Toronto Dermatology Centre

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