What is the X in X-mas?
1753, from Greek ekzema, literally "something thrown out by heat," from ekzein "to boil out," from ek "out" (see ex-) + zema "boiling," from zein "to boil," from PIE root *yes- "to boil, foam, bubble" (see yeast). Said to have been the name given by ancient physicians to "any fiery pustule on the skin."
eczema ec·ze·ma (ěk'sə-mə, ěg'zə-, ĭg-zē'-)
An acute or chronic noncontagious inflammation of the skin, characterized chiefly by redness, itching, and the outbreak of lesions that may discharge serous matter and become encrusted and scaly.