VOC's stands for "Volatile Organic Compounds (VOC's) are organic chemicals that have a high vapor pressure and easily form vapors at normal temperature and pressure."
those Vapors can be absorbed and cause as headaches and even worse up to shortening a person's life expectancy. In this day in age there are options to limit and even use paints that have Zero VOC's such as Harmony from Sherwin Williams or Everist from Dunn Edwards.
With health in mind and the choice is simple for a house painter to pick these options not only that but also they look great and last long without the headache from toxic paint.