New regulations governing the sale of electronic cigarettes in Massachusetts take effect this week. As of Friday, anyone under 18 years old is barred from buying e-cigarettes. The regulations also ban the promotional giveaway or free distribution of e-cigarettes and require that they be kept out of the reach of customers. Attorney General Maura Healey said the regulations also ban most sales of e-cigarettes except through face-to-face purchases; sales through vending machines are permitted only in adults-only establishments. E-cigarettes are battery-powered devices that turn nicotine-containing liquid into vapor that is inhaled. Though nicotine can be addictive, e-cigarettes lack the chemicals and tars of burning tobacco.