One problem the late 1990 and early 2000 Camary engines seemed to suffer from is oil seeping down the valve stems while the engine sits. It seemed to affect the 4 cylinder engines, specifically the 5S-FE engine. Sometimes it is regular but other times it is intermittant. The smoke is greyish white and lasts until it drifts away.
I suspect that the smoke is white because the oil gets past the exhaust valve seal(s) and drips down the stem(s). When the engine starts the oil is vaporized and comes out white since it is not burned in the combustion chamber. This oil loss does not appear to affect the engine’s oil consumption noticeably. So far it has not affected my catalytic converter, although that is an area of concern.
The valve stem seals can be replaced without removing the head but it does require removing the cam shafts which means the timing belt or chain must be removed.
Hope this helps.