Urushiol, is the rash-causing oil found in all parts of poison ivy, poison oak, and poison sumac plants. Approximately 85% of the population experiences an allergic reaction to these noxious plants, and according to the National Institute of Occupational Health & Safety, 50 micrograms of urushiol is enough to cause a rash in 80-90% of adults.
Sweaty palms, more properly known as palmar hyperhidrosis, is a condition that affects about 1% of the US population. Although the exact cause of sweaty palms is still debated, many experts believe it is caused by a hyperactive sympathetic nervous system, causing the sweat glands in the hands to produce sweat unnecessarily.
Sometimes a callus occurs where there is no rubbing or pressure. These hyperkeratoses can have a variety of causes. Some toxic materials, such as arsenic, can cause thick palms and soles. Some diseases, such as syphilis, can cause thickening of the palms and soles as well as pinpoint hyperkeratoses.