All mammals have hair and it is normal to moult periodically as a means of getting rid of old hairs and replacing them with new ones. The hedgehog's relatives, the moles and shrews, moult twice per year. The long, thick winter coast is shed in spring to be replaced by summer fur. In the autumn, this is lost and a new winter coat is grown as longer denser fur becomes more necessary. The hedgehog is less concerned to keep itself warm in winter and would find it highly inconvenient to moult all its spines twice a year; they would take too long to replace. In practice, hedgehogs moult the same way we humans do. Each hair and spine follicle has its own rate of growth and is not synchronized with its neighbours. So spines and hairs and being grown and lost continuously, one or two at a time, not in a big co-ordinated seasonal moult. In shres and moles and individual hair has a 'service life' of only six months till the next moult. In few mammals do the individual hairs persist longer than a year. By contrast, each of the hedgehog's spines may last well over a year, perhaps more than 18 months, before it finally falls out and a replacement is grown.