why is it so important to cover one's head in rain

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I was on my way to a close by cafe today and my maidservant asked me to cover my head with something if i do not want to carry a umbrella.. she told me it is important to cover the head does'nt matter if the body gets wet it's the same with heat as well i mean we are asked to carry a umbrella wear a cap when it's very sunny or humid outside... also covering the eyes is important...