hair loss - please help!

hello everyone, just wondering if anybody could help me out here...

my beautiful black cat alfie has recently developed patches of hair loss on his flanks below his hips, also a little in his genital area. it's not completely bald - it sort of looks like cat's hair does after a few weeks of regrowth when a vet's shaved a spot?

he's normally a very very healthy boy - spends all day running around an orchard by the river, eats well, very friendly, keeps himself nice and clean, top cat in the neighbourhood and everyone always remarks on how glossy and good he looks. apart from breaking his hip falling out of a tree as a young kit, he's never had to go to the vet. we really couldn't ask for a better cat and he means the world to us so to see him looking poorly is really worrying.

we thought it might be a flea allergy so we've made sure he's had his frontline / program protection (the kind that goes in his food) and we thought we'd wait a while and see if it clears up. but looking online has got me worried - i've read about hyperthyroidism. How common is this? Is it easily treated? He doesn't seem to have stopped grooming himself, and I don't think he's lost weight. As for insatiable appetite... he's an active 3 year old male - he's always mewing for food!

We'll take him to the vets if it doesnt clear up soon, but I just wondered if anyone could share their wisdom with me re. hair loss / other reasons he could be looking a bit shabby. I'd really really appreciate it, it's so worrying when a super healthy cat looks out of shape Thanks a million xxx

Sometimes hair loss is related to stress and sometimes the cat tears his/her fur out because of stress or because of military dermatitis (allergy to fleas). Does he seem stressed to you? And/or do you find any fleas on him using a flea comb?

thanks Tarasgirl06. no he's never seemed stressed - no big changes to his routine; he pretty much just spends all day running around outside or napping around the house - he's super laid back.

i'm a student so i come and go a lot, but he's a family pet so everyone else is pretty constant in his life and me being away's never seemed to affect him before. no fleas on him that we can see (me and mum get bitten if there's one within a mile radius normally so im inclined to believe he's fleafree!)

Is he overweight? Sometimes cats that are overweight have skin issues.