Scotch whiskies are generally distilled twice, though some are distilled a third time. International laws require anything bearing the label "Scotch" to be distilled in Scotland and matured for a minimum of three years and one day in oak casks, among other, more specific criteria. If Scotch whisky is from more than one cask, and if it includes an age statement on the bottle, it must reflect the age of the youngest whisky in the blend. Many cask-strength single malts omit the age as they use younger elements in minute amounts for flavouring and mellowing. The basic types of Scotch are malt and grain, which are combined to create blends. Many, though not all, Scotch whiskies use peat smoke to treat their malt, giving Scotch its distinctive smoky flavour. While the market is dominated by blends, the most highly prized of Scotch whiskies are the single malts. Scotch whiskies are divided into five main regions: Highland, Lowland, Islay, Speyside and Campbeltown.