Background
Ageing reduces the resting blood flow to the skin as well as the blood flow response to thermal stimuli. However, the interrelationships between skin thickness, subcutaneous fat, and skin blood flow in determining the heat dissipation characteristics of the skin have not been investigated.
Material and Method
In the present investigation, 60 male and female subjects were examined with either a continuous 0.15 watt heat source or a 40 degrees C instantaneous heat source applied to the skin. Data was correlated to skin and subcutaneous fat thickness measured by ultrasound and to skin blood flow measured by a laser Doppler flow meter.
Results
The results of the experiments showed a significant negative correlation between age and skin thickness (p<0.0001) and between age and subcutaneous fat thickness (p<0.001). Blood flows in the skin, with the subject in a 24 degrees C, room were 61.8% less in the older subjects compared to the younger subjects. This was due to both a reduction in red cell concentration and red cell velocity. The lower concentration of red cells matches the reduction in skin thickness, implying a loss in the dermal layer of the skin associated with ageing. The skin blood flow response to continuous heat and to a single heat exposure were both reduced in the older subjects (p<0.01). Ageing also caused a slower response of the skin to heat stress.
Conclusions
The results support a reduction in both the resting and post local heat skin blood flows associated with ageing. Some of this may be due to a reduction in dermal layer thickness due to ageing.

Keywords: Skin Aging - physiology, Skin - blood supply, Rest, Regional Blood Flow, Hot Temperature, Body Weight, Body Mass Index, Body Height, Aged, 80 and over, Skin Physiological Phenomena, Skin Temperature - physiology