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.
Psoriasis can cause itching and the formation of white pustules on the palms and soles. It often spreads to the fingernails and toenails. About 25 percent of people who have hepatitis B or hepatitis C develop palmoplantar pruritis. Itchy hands and feet can be an expression of gallbladder disease.