They could be caused by heat or they could be caused by water. Either way, the white marks on your wood table may be a source of stress but shouldn’t be cause to throw the table away. This is a science project disguised as a home repair project. So head to your “labs” -- your kitchen and bathroom -- and reach for several common household products. Try one or try several until those white marks fade for good.
Rub mayonnaise into the white marks. As you do so, the white marks may disappear. If they don’t, let the mayonnaise sit on the white marks for at least one hour. Wipe the table with a clean, dry cloth.
Rub some non-gel toothpaste into the white marks. If they don’t disappear with the swipe of a clean rag, combine the toothpaste with a little baking soda and rub the mixture into the marks. Wipe the table clean.
Dampen a clean rag and sprinkle it with a little baking soda. Rub the mixture into the white marks until they disappear.
Coat the white marks with vegetable oil, petroleum jelly or a thin paste of olive oil and salt. Let the oil sit on the table overnight, and wipe with a clean, dry cloth.
Treat the most stubborn white marks with 0000 steel wool and a little lemon oil. Buff the white marks in the direction of the wood grain on the table until the white marks disappear. Keep in mind that the sheen of the rest of the table might look dull by comparison, requiring you to apply lemon oil to the rest of the surface.
Buff the table in a circular motion with a clean cloth to restore its natural shine. Follow with a good furniture polish to protect it.