---
title: "Photodynamic Therapy"
---
[Actinic keratoses](/conditions/actinic-keratosis/) are the rough, scaly patches that show up on the parts of you that have taken the most sun: the forehead, the nose, the tops of the ears, the scalp if your hair has thinned, the backs of the hands. They are precancerous, which means some of them go on to become a squamous cell carcinoma if they are left alone. [2] More than 40 million Americans develop them each year. [2]
The usual approach is to freeze the ones you can see, one at a time. That works well when there are a few. When [years of sun](/conditions/sun-damage/) have left a whole region of skin damaged, freezing spot by spot becomes a game of catch-up, because for every patch you can feel there are usually others that have not surfaced yet.
Photodynamic therapy treats the region instead. A solution is applied across the whole area and absorbed preferentially by the damaged cells. A blue light then activates it, and those cells clear as your skin heals over the following one to two weeks. You come out with new skin across the area rather than a handful of treated spots and the same problem underneath.
**What photodynamic therapy is used for**
- Actinic keratoses on the face and scalp, treated as a whole area at once
- Sun-damaged regions where new rough patches keep appearing
- Scalps where thinning hair has left skin exposed for years
- People who would rather have two appointments than a standing series of freezing visits
- Reducing the risk that a precancerous growth becomes a skin cancer [1]
This is the part worth understanding before you choose between treatments, because it is the whole reason photodynamic therapy exists alongside freezing.
Sun damage does not arrive one spot at a time. It accumulates across a region over years, and the rough patch you can feel today is simply the one that surfaced first. Dermatologists call treating the whole region **field treatment**, as opposed to **lesion-directed treatment**, which handles the individual growths you can see.
Freezing, spot by spotPhotodynamic therapy, whole areaWhat it treatsThe growths you and your dermatologist can see and feelThe visible growths and the surrounding damaged skin they came fromBest whenYou have a small number of scattered patchesA whole region keeps producing new onesAppointmentQuick, often part of a routine visitAround two hours, most of it waitingAfterwardSmall blisters or scabs on each treated spot48 hours indoors, then redness and peeling across the areaHow oftenRepeated whenever new patches appearUsually two treatments, a few weeks apart
Neither one is better in the abstract. If you have three patches, freezing them is quick and sensible. If you have been back three times in two years and there are always more, treating the field is usually what breaks the cycle. Your dermatologist will tell you which situation you are in, and it is a straightforward conversation.
Before any treatment is planned, the area is examined by a board-certified dermatologist. Rough, scaly patches are usually actinic keratoses, and sometimes they are something that needs a different answer entirely. Telling those apart is the work, and it is why this is done in a dermatology practice rather than anywhere a light can be plugged in.
It also means the treatment sits inside a longer view of your skin. Anyone with enough sun damage to need field treatment is someone whose skin is worth watching over time, so photodynamic therapy is usually one part of a plan that includes [a skin cancer check](/treatments/skin-cancer-diagnosis/) and [daily sun protection](/treatments/heliocare/). That plan is what keeps you ahead of it.
**Photodynamic therapy is often the right choice if:**
- You have several actinic keratoses across one region rather than one or two isolated patches
- New rough patches keep appearing in the same area after freezing
- Your scalp or face has taken decades of sun and the damage is widespread
- You can arrange to stay indoors for the 48 hours afterward [1]
**Your dermatologist may suggest something else if:**
- You have only a few isolated patches, where freezing is quicker and simpler
- You are taking a medication that makes your skin unusually sensitive to light
- You have a condition that makes light-sensitive treatment unsuitable
- The 48 hours indoors will not fit the next few weeks, in which case it is worth waiting for a week that suits
All of this is settled at your appointment, after your skin has been examined. There is nothing you need to work out in advance.
The 48 hours after treatment matter more here than the treatment itself. Your skin stays highly sensitive to light during that window, including daylight through a window or on an overcast day, so you stay indoors and away from bright indoor light. [1] After that, expect redness, some swelling and peeling across the treated area for several days, similar to a strong sunburn, as the treated cells clear and new skin comes through.
**In the first 48 hours, do**
- Stay indoors and out of daylight completely, including on cloudy days [1]
- Keep the treated area covered if you have to go outside at all
- Use a gentle cleanser and whatever ointment we send you home with
- Plan the treatment for a stretch when two days indoors is easy
**In the following week, do**
- Let any flaking and peeling come away on its own
- Wear broad-spectrum sunscreen, SPF 30 or higher, every day from then on [3]
- Keep your follow-up appointment, because the second treatment is part of the plan
- Tell us about anything that does not match what we described
Call us about anything severe, worsening or unexpected: significant pain, blistering, spreading redness, or signs of infection. We would far rather hear from you early.
Sun-damaged and precancerous skin, treated across the whole area. Pick a concern to see how we approach it.
Photodynamic therapy is a medical treatment rather than a cosmetic one, so the cost depends on the area treated and the number of sessions, and it is handled differently from the aesthetic services on this site. Our office will go through what applies to you before anything is scheduled.
If freezing a few patches would serve you just as well, that is what will be recommended, and it is the less involved appointment of the two.
**Q: Why does the appointment take two hours?**
Most of it is waiting. The solution needs around 60 to 90 minutes on your skin before the light, so it can concentrate in the cells being treated. [1] The light itself is a fraction of that. Bring a book.
**Q: Does it hurt?**
Most people describe a stinging, burning or prickling sensation during the light portion, strongest in the first few minutes and easing after that. It is manageable, we can cool the area as we go, and it stops when the light does.
**Q: Why do I have to stay indoors for two days?**
Because the solution leaves your skin very sensitive to light for about 48 hours, and daylight during that window can cause a strong reaction, even on a cloudy day. [1] It is the one instruction that really matters, and planning the treatment for a quiet couple of days makes it easy.
**Q: How many treatments will I need?**
Most patients need two, with the second given a few weeks after the first. [1] Your dermatologist will confirm what your skin needs after examining the area.
**Q: Will the patches come back?**
New actinic keratoses can appear in sun-damaged skin over time, which is why this is usually paired with regular skin checks and daily sun protection. Treating the field puts you well ahead of where you were, and keeping up with checks is what holds that position.
**Q: Do I need a referral?**
Yes. Photodynamic therapy is medical dermatology, and the practice is currently accepting new medical patients by referral from your primary care physician. Once you have that, call the office and we will get you booked.
Both offices offer photodynamic therapy. San Luis Obispo uses blue light and Santa Maria uses red light.
1. American Academy of Dermatology Association. "Actinic keratosis: Diagnosis and treatment." States that treatment can "reduce your risk of developing skin cancer," that during photodynamic therapy "a solution that makes your skin extremely sensitive to light is applied to the area with AKs. You'll sit in the office with this on your skin for about 60 to 90 minutes. Afterward, you'll be treated with either a blue or red light," that "for 48 hours after treatment, you'll need to avoid the outdoors during daylight. The UV light, even on a cloudy or snowy day, can cause a serious skin reaction," and that "most patients with AKs need 2 PDT treatments, with the second treatment given 3 weeks after the first." [https://www.aad.org/public/diseases/skin-cancer/actinic-keratosis-treatment](https://www.aad.org/public/diseases/skin-cancer/actinic-keratosis-treatment) · Medical Organization
2. American Academy of Dermatology Association. "Actinic keratosis: Overview." Describes an actinic keratosis as "a precancerous skin growth caused by the sun or indoor tanning," states that "more than 40 million Americans develop actinic keratoses each year," and that "some AKs and actinic cheilitis turn into a type of skin cancer called squamous cell carcinoma." [https://www.aad.org/public/diseases/skin-cancer/actinic-keratosis-overview](https://www.aad.org/public/diseases/skin-cancer/actinic-keratosis-overview) · Medical Organization
3. American Academy of Dermatology Association. "How to select a sunscreen." Broad spectrum, SPF 30 or higher, water resistant. [https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/how-to-select-sunscreen](https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/how-to-select-sunscreen) · Medical Organization
Content on this page is for educational purposes and is not a substitute for professional medical advice. Redness, swelling, stinging during treatment, and peeling across the treated area for several days are expected. Treated skin is highly sensitive to light for approximately 48 hours after treatment and must be kept out of daylight during that period. Blistering, infection, and temporary lightening or darkening of the skin are uncommon but possible. Tell us about any medication that makes your skin sensitive to light. This treatment is not suitable during pregnancy or where there is a known sensitivity to the medication used. Individual results may vary.
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