Generally, radionuclides do not cross the intact skin to any significant extent. Exceptions of practical importance are tritium oxide as liquid or vapour, organic carbon compounds and iodine as vapour or in solution.
There is no general model of entry of radionuclides through the skin because of the large variability of situations which may occur. Skin can become contaminated by contact with aerosols, liquids or surfaces contaminated with radionuclides. Clothing may be an important source of skin contamination and wet clothing may bring the contaminant into close contact with the skin thereby increasing the possibility of penetration through it. Many factors must be taken into account in dose assessment: the chemical form of the compound, the location and the surface of the contaminated area as well as the physiological state of the skin. Intact skin is a good barrier against entry of a substance into the body.
For skin contamination, both the radiation dose to the area of skin
contaminated and the dose to the whole body as a result of absorption need to be considered. ICRP in Publication 60  has recommended that for skin contamination doses should be calculated to
sensitive cells, assumed to be at a depth of 70 μm (as a reasonable average value). For deposited activity doses are to be calculated as an average to each cm2 of skin tissue. This
applies to activity distributed over the skin surface or aggregated in particles. No specific models are recommended by ICRP for calculating doses from β particles deposited on the skin and
absorbed through it.