Objective
This study was designed to assess the influences of skin temperature and age on latency and amplitude of the sympathetic skin response (SSR).

Method
We examined the sympathetic skin responses in 77 normal subjects aged 25 to 73 years. With stimulation of both median nerve and both tibial nerve at the wrist and ankle, the SSRs were recorded from both palms and soles simulaneously. To determine the effects of skin temperature change on SSR, we examined the SSRs in 12 healthy subjects before and after heating. The heat was applied on right forearm by infra-red lamp.

Results
The mean latency and the mean amplitude of SSR with stimulation of the right median nerve at the wrist were 1.47 sec and 6.08 mV at the right palm, 1.50 sec and 6.07 mV at the left palm, 1.95 sec and 3.38 mV at right sole, and 1.95 sec and 3.09 mV at left sole. There was no side-to-side difference in the latency and the amplitude. Regardless of the site of stimulation, latency was longer at the sole than at the palm, and amplitude was greater at the palm than at the sole (p＜0.05). The latency of the SSR was positively correlated with the age of subjects (p＜0.05), and the amplitude was negatively correlated with the age of subjects (p＜0.05). At higher skin temperature, the latency of SSR was shortened and the amplitude was reduced significantly (p＜0.05).

Conclusion
The amplitude of the SSR decreases with aging and the latency increases with aging. As the skin temperature rises, the latency and amplitude show tendency to decrease. We suggest that the skin temperature and age are important factors to be considered carefully in assessing the SSR parameters.