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One thousand and forty people aged 40 years and over, 616 (59.2%) of whom had solar keratoses, were followed for 12 months. Two hundred and twenty-four people (36.4%) had a spontaneous remission of at least one of their solar keratoses. A total of 485 lesions (25.9%) underwent spontaneous remission out of the 1873 lesions that were present at the first examination of these 224 people. There was no significant difference between the number of lesions present at the initial examination in those who had a spontaneous remission compared with those who did not. There was a 21.8% increase in the total number of solar keratoses in the 1040 people studied in the 12-month period, due to new lesions forming at the same time as remissions were occurring. The incidence rate of squamous cell carcinoma occurring in the people with solar keratoses was 0.24% for each solar keratosis present at the original examination. With a substantial proportion of solar keratoses remitting spontaneously, plus the low rate of malignant transformation and the low potential for metastasis to occur from squamous cell carcinoma arising in a solar keratosis, the rationale of treating all solar keratoses appears questionable.

The reproducibility of the pulsed ultrasound technique for the determination of skin thickness was investigated, using two independent observers. No systematic difference was found and a high correlation was obtained. Studies were also undertaken to validate the pulsed ultrasound technique as a measure of true skin thickness. Skin thickness determined in vitro was found to be greater than when in vivo determinations were made by either the pulsed ultrasound or a xeroradiographic technique, probably due to the release of in vivo tension within the dermis after excision. Skin thickness was found to increase linearly with age up to the age of 20 years and to decrease linearly with age subsequently. Differences in skin thickness between the sexes and in different sites of the body were demonstrated.