The healing power of light

National report - Light therapy has been used in dermatology for a long time and remains firm in the armamentarium for the treatment of various dermatoses. The range of indications for using light in dermatology spans all areas including chronic inflammatory dermatoses, pigmentary disorders, cancer, infections and cosmetic applications. Iltefat H. Hamzavi, M.D., senior staff physician in the department of dermatology at Henry Ford Hospital in Detroit, shared his significant experience in light-based therapies, their indications, and the importance of their use in dermatology.

Understand light, skin

In order to understand how to get light to the skin one must understand that the interaction of light with tissue is governed by three basic processes that can occur when a photon of light reaches the skin: reflection, scattering and absorption. Absorption is an important biophysical event that involves the transfer of energy from light to tissue. Without photon absorption, energy will not be taken up by the skin, and no biologic or therapeutic effect will occur. Both scattering and absorption determine the depth to which light will penetrate the skin, but only absorption leads to photobiologic and phototherapeutic effects.

Dr. Hamzavi says, "For any clinical indication, a multiplicity of possible photonic devices are often available. This simply reflects the fact that, from the point of view of the tissue and its chromophores, the exact source of the photons (e.g. laser vs. intense pulsed light vs. light-emitting diode vs. fluorescent lamp) matters far less than whether the photons are of the appropriate wavelength and delivered to the target in sufficient quantity to cause irreversible tissue changes."

Lasers, IPL

Lasers and IPL devices are based on selective destruction of an undesirable component of the skin. They are based on the basic principles of skin optics. First, decide what structure you want to eliminate, then decide what photons it tends to absorb, and then figure out how you want to heat the structure without damaging the surrounding tissue. Selecting the wavelength, the pulse duration (how long the device will heat up the target) and the appropriate cooling device allows a laser operator to safely and effectively target components of the skin such as blood vessels, hair, pigment and tattoos.

UV light as immunomodulator

Recent advances in ultraviolet phototherapy include a better mechanistic understanding of its biologic effects, more rational dosimetry approaches and the deployment of several novel UV sources. Dr. Hamzavi says the basic science for UV phototherapy is characterized best for psoriasis where the induction of T-cell apoptosis has been demonstrated for broad and narrow band UVB as well as PUVA. Here, T-cell-depleting effects are likely pivotal for clearing inflammatory dermatoses and cutaneous T-cell lymphoma.

"In conventional UV phototherapy, both diseased and normal skin are exposed to light. While the primary goal for treating inflammatory dermatoses such as psoriasis is to clear skin lesions using light, our current approach to UV dosimetry is limited by the need to avoid burning the unaffected skin," Dr. Hamzavi explains.