Skin is the largest organ of the body and, as such, is at the greatest risk for coming in contact with the laser beam.  The most likely skin surfaces to be exposed to the beam are the hands, head, or arms.


Lasers can harm the skin via photochemical or thermal burns.  Depending on the wavelength, the beam may penetrate both the epidermis and the dermis.  The epidermis is the outermost living layer of skin.  Far and Mid-ultraviolet (the actinic UV) are absorbed by the epidermis.  A sunburn (reddening and blistering) may result from short-term exposure to the beam.  UV exposure is also associated with an increased risk of developing skin cancer and premature aging (wrinkles, etc) of the skin.


Skin Components


 


skin schematic



  • Stratum Corneum (Dead Layer)

    • The stratum corneum is the outermost layer or the horny layer. It consists of flattened, dead epidermal cells that protect the living tissue from water loss, injury from physical objects, and radiant energy. The thickness is 8-20 um except on the soles of the feet and the palms of the hands where it is 500-600 µm.

  • Epidermis

    • The epidermis is the outermost layer of living tissue, where the tanning process takes place. It has a relatively uniform thickness of about 50-150 µm.

  • Dermis Corium

    • The dermis corium is made up largely of connective tissue which gives the skin its elasticity and supportive strength. Included in this layer are nerve cells, blood vessels, and lymphatic glands. The thickness of this layer varies over the body from 1-4 mm.

  • Subcutaneous Tissue

    • The subcutaneous tissue is made up mostly of fatty tissue serving as insulation and as a shock absorption medium. The thickness of this layer varies according to the area of the body as well as from person to person.

How Does Laser Light Affect the Skin?


Laser effects on tissue depend on - the power density of the incident beam, absorption of tissues at the incident wavelength, time beam is held on tissue, and the effects of blood circulation and heat conduction in the effected area.


wavelength vs. penetration


As indicated by the illustration above, different wavelengths of light penetrate the skin in different ways. At approximately 750 nm, absorption to the subcutis occurs.


Tissue Damage from a CO2 Laser


 


hot dog


250 Watt Laser Moving at 1 Inch per Second


chicken with laser burns


250 Watt Laser in Single Pulses


Immediate Effects


As shown above, the immediate effect of exposure to laser light above the biological damage threshold is normally burning of the tissue.  Injury to the skin can result either from thermal injury following temperature elevation in skin tissues or from a photochemical effect (e.g., "sunburn") from excessive levels of actinic ultraviolet radiation.


Some individuals are photosensitive or may be taking prescription drugs that induce photosensitivity.  Particular attention must be given to the effect of these (prescribed) drugs, including some antibiotics and fungicides, on the individual taking the medication and working with or around lasers.
 


Delayed Effects


The possibility of adverse effects from repeated or chronic laser irradiation to the skin has been suggested, although it is normally discounted.  Only optical radiation in the ultraviolet region of the spectrum has been shown to cause long-term, delayed effects.  These effects are: accelerated skin aging and skin cancer.  At present, laser safety standards for exposure of the skin attempt to take these adverse effects into account.


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