Hi there. There is a possibility that this is being caused by vitamin A deficiency in the diet. The symptoms of vitamin A deficiency include a dry and flaky cere(and sometimes also beak), and also it can sometimes appear as if growths are appearing within the cere and beak, due to the deficiency in the vitamin affecting the structure of the keratin that forms these structures.
It's important that Parakeets are never fed entirely on seed mixes, as this is usually how this deficiency arises- there is some information available on feeding and vitA deficiency at this link
www.barkrescue.net/parakeetcare.htm
the main issue if this is occurring is to amend the diet so that the correct balance of minerals and vitamins is being given, before the bird becomes ill in itself. Once a balanced diet is being fed, the structure of the keratin, and hence the cere and beak, will improve.
Andrea
Bird Veterinarian
15 years in companion animal practise, BVM&S degree Edinburgh university