Nice hams turned nasty.

[Noodle]

I've had my cambells about 7 months now, and they're both fully tame. However, a couple of weeks ago my hamster Milbert was biting non stop very hard which lasted around a week. He's now just as he was before, gentle and cuddley. Today, my other hamster Muphy has started the same thing. It really hurts! He still wants to come out and play, but whenever I get him, *BITE*.

Does anyone know of a cycle they might be in?!

Oh and I haven't changed handwash, and do make sure my hands are washed before handling.