DS is 7 mo but still has a bald patch on the back of his head.
He's had it from not long after birth, seems to be from lying in his cot as it was right where the back of his head rests on the mattress - but he spends most of his waking time sitting up now so I can't work out why it's not improving. The rest of his hair is thickening up well. Doesn't bother me but occurred to me today and wondered if it's common?