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The commonest cause of nails breaking is iron deficiency
and other reasons can be fungal infection;hypothyroidism;Raynauds phenomena where the arteries of arms and legs get affected;prolonged exposure to cold
weather;application of nail polish remover etc.So better first get tested to find the haemoglobin
and if possible thyroid test.Also start having vitamins and minerals
tablets and if the haemoglobin is low you will need to take iron tablets.