Zinc oxide fumes. From
http://www.weldweb.com/safety.php?articleID=8:
Zinc oxide fumes cause a flu-like illness called Metal Fume Fever. Symptoms of Metal Fume Fever include headache, fever, chills, muscle aches, thirst, nausea, vomiting, chest soreness, fatigue, gastrointestinal pain, weakness, and tiredness. The symptoms usually start several hours after exposure; the attack may last 6 to 24 hours. Complete recovery generally occurs without intervention within 24 to 48 hours. Metal Fume Fever is more likely to occur after a period away from the job (after weekends or vacations). High levels of exposure may cause a metallic or sweet taste in the mouth, dry and irritated throat, thirst, and coughing at the time of the exposure. Several hours after exposure, a low-grade fever (seldom higher than 102º F or 39º C). Then comes sweating and chills before temperature returns to normal in 1 to 4 hours. If you encounter these symptoms, contact a physician and have a medical examination / evaluation. There is no information in the literature regarding the effects of long-term exposure to zinc oxide fumes.
Electric melting will cause fewer fumes because of lower temperatures involved versus flame melting. Be sure to have a fume hood that exhausts out of doors when melting zinc.