Light penetration into skin

Beta particles are normally faster than alpha particles and not as easy to stop. For this reason, they are able to penetrate light materials such as paper and clothing. They can penetrate fairly deeply into skin, where they have the potential for harming or killing cells. They are not able to penetrate deeply into denser materials, however, such as aluminum. Beta particles, once stopped, become part of the material they are in, like any other electron. 

The total amount of incident fluence rate penetrating into the skin is broken into portions of reflected, absorbed, transmitted and scattered light. Figure 3 shows the transmission of the skin for scalp skin of different hair color. For the skin with blonde hair the transmittance was 92.4 %, but for light brown and black hair the transmittance was 91.82 % and 90.9 % respectively, at a depth of 0.02 mm. The epidermal transmittance was 67.5% for the blonde hair and 65.6 %, 63 % for the light brown and black hair respectively, at a depth of 0.08 mm, (Fig. 1). The loss of injection dose from skin depths Z=0.02 mm to 0.08 mm for skin with the blonde, light brown and dark hair are 25, 26 and 28 %, respectively. 

An activation photosensitizer, laser and relation color of hair appeared as a task factors to change photodynamic dose rate and this is one of the most challenging problems in the field of PDT for epidermis layer, both in terms of research and of development. Consideration of hair color during therapy will increase the quality of PDT treatment in patients. Our results demonstrated and concluded that the types of a hair color, concentration, and penetration depth into the skin affect the absorptive and scattering processes to impact photodynamic dose in PDT for superficial diseases. Computation simulation considerations show that the effect of hair of different colors is affecting light penetration and dose injection. 

By definition photoaging involves UVR (200-400 nm) [4] exposure, mainly from the sun but also from therapeutic sources of UVR and tanning salons. Ultraviolet C (UVC, 200-290 nm) is the most biologically damaging portion of the UVR spectrum but is almost entirely absorbed by the ozone layer of the earth s atmosphere. The strongest ultraviolet light to reach the earth s surface is ultraviolet B (UVB, 290-320 nm). Ultraviolet A (UVA, 320-400 nm) has greater penetration into the skin but is much weaker than UVB. 

The penetration of light into and through dermal tissues has important consequences. This penetration is demonstrated in Fig. 11.1. Skin, as the primary organ responsible for thermal regulation, is overperfused relative to its metabolic requirements (Anderson and Parrish, 1981). 

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