Reduced Side-Effects of Photodynamic Therapy for the Treatment of Moderate to Severe Acne (i-PDT)

Inclusion criteria 1. Subjects with ages between 14 and 50 years, male or female. 2. Subjects with severe acne lesions (one or more nodules or cysts present) on their backs or face 3. Presence of moderate acne on the back and/or face that has been recalcitrant to previous treatments. Recalcitrant acne is acne with no or mild/temporary (less than 3 months) improvement after using: * Accutane® for at least one completed treatment cycle, and/or * Oral antibiotic for ≥ 3 months; and/or * Topical prescription retinoids (tretinoin - retinoic acid, adapalene, tazarotene or other derivatives) for ≥ 3 months, and/or * Topical benzoyl peroxide 2.5% or higher concentrations for ≥ 3 months * Hormonal treatments\*\* for ≥ 3 months. 4. Willingness to participate in the study 5. Willingness to receive ALA-PDT treatment 6. Informed consent agreement signed by the subject 7. Willingness to follow the treatment schedule and post treatment care requirements 8. Willingness to not use topical or systemic (oral) anti-acne medications including medicated shampoo or soap during the study period. Exclusion criteria 1. Subjects receiving concurrent oral retinoids or antibiotics \*\* Subjects with chronic use of antibiotics may be included if proven that its use has not changed the severity of their acne. AND \*\*\* Chronic use of antibiotic is considered ≥ 2 years of continuous use. 2. Scarring or infection of the area to be treated 3. Known photosensitivity 4. Presence of suntan in the area to be treated 5. Subjects who have taken medication known to induce photosensitivity in the previous 3 months 6. Subjects who have had prior oral retinoid (Accutane®) use within 6 months of entering the study 7. Prior oral antibiotic use within 1 month of entering the study (see exclusion #1) 8. Topical antibiotic or other topical anti-acne treatments use within 2 weeks of entering the study 9. Known anticoagulation or thromboembolic condition 10. Subjects who are immunosuppressed 11. Subject is unable to comply with treatment, home care or follow-up visits 12. Subject is pregnant or breast feeding 13. Subject has a history of being on photosensitive medications (thiazides \[used to treat high blood pressure\], tetracyclines, fluoroquinolones griseofulvin or sulfonamides \[used to treat infections\], sulfonylureas \[used to treat diabetes\], calcium channel blockers \[used to treat hypertension\]. phenothiazines \[used to treat serious emotional problems\]). 14. Known skin sensitivity to blue light 15. Porphyria (a disorder of the metabolism that can lead to sensitivity to light) 16. Allergies to chemicals called porphyrins 17. Subjects who started hormonal treatment (for medical conditions or birth control) within less than 3 months.