Shedding
Most dogs shed or "blow" their coats at least once a year. Females sometimes blow their coats after they've been in season, during pregnancy, or after nursing.
Some dogs have a double coat composed of a long outer coat of guard hair and an under coat of soft woolly hair. When a dog with a double coat begins to shed, his appearance may be quite alarming and at first suggests a skin disease. This is because the inner coat is shed in a mosaic or patchy fashion giving rise to a moth-eaten look. This is perfectly normal. Dogs do not shed their coats evenly or in waves.
Coat loss is occasionally precipitated by sudden physical stress or illness, pregnancy, or changes in the internal balance of hormones. Stressful conditions causing hair to drop out first appear where hair grows the fastest, on the body and flanks; as opposed to the hair on the legs which grows the slowest.
Many people believe that it is the seasonal change in temperature which governs when a dog sheds his coat. But, in fact, shedding is influenced more by changes in surrounding light. The more exposure to light, the greater the shedding. This is why house dogs, exposed to long hours of artificial light, seem to shed excessively.
When shedding begins you should attempt to remove as much of the dead hair as possible by daily brushing. With some breeds that have thick double coats, bathing will help to loosen the dead hair and make it easier to remove by brushing. Dead hair next to the skin is irritating to the dog. It often leads to an itch-scratch cycle which damages the skin and may cause further skin problems.