You should take the sun very seriously in all of Argentina. The north of the country is one of the hottest regions of Latin America in summer -temperatures regularly hit the 40 degree mark and the extended siestas taken by locals are a wise precaution against the debilitating effects of the midday heat. Where possible, avoid excessive activity between about 11am and 4pm and where you do have to be out in the sun, wear sunscreen and a hat. You should also drink plenty of liquids - but not alcohol - and always make sure you have a sufficient supply of water when embarking on a hike. Throughout the country, the sun can be extremely fierce and even people with darker skin should use a much higher factor sunscreen than they might normally: using factor 15 or above is a sensible precaution