Friendly hamster turned aggresive?

Question
I know that hamsters housed together sometimes will fight
and needs to be separated. I have 2 dwarfs and they were
living together harmoniously for the past 2 months and the
younger one is always very tame, I can even handle her and
she doesnt bite.
Just today, after I cleaned up the cage and put both back
in.. the tamer one started to fight with the other hamster
for no apparent reason. They were good all along. I dont
know what triggered this, but now one has a bite mark and
he's kind of wary when the tamer hamster whenever he's
around.
Why is there a sudden 360 change? Could it be because of the
lost of their scents after I cleaned the cage?

Thanks!

Answer
Hi Mandy

sorry to hear your hamsters aren't getting on.  I don't know if there is any logical reason when this happens.  I've had a group of gerbils before who were all fine, then one day they were biting each other.  It is hard to pinpoint what has caused the sudden agression.  

With your hamsters it could be that they have now reached adulthood and this is why the situation has changed. One will always want to be dominant, but if they have always been together and are related then often they are fine, but in some situations they aren't.  Unfortunately once they start fighting like this there is no going  back.  As one has been bitten and is wary of the other, if you leave them together they will continue to fight and the one with the bite will be bullied.  It is a very difficult decision to make and one you need to give careful consideration, but if the quality of life of one is poor due to being bullied and afraid of the other one, then the kindest thing would be to separate them.  Once separated, however, you can not re-introduce them.  If the they continue living together then the fighting could become much more serious - but in the end the decision to separate them is very much up to you.

sorry I can't give you any straightforward explanation.

Regards
Sheila