I have a collie pup and from not long after I got her (at 11 wks - she's 5 months now) I kept seeing her licking one patch on one of her front legs and the fur became a little thinner - then the behaviour seemed to stop - I never told her off for it - only tried to distract her with toys so don't think she would hide it from me.

Initially I thought this must be related to anxiety to do with her severe car sickness as she settled in so well which is why I didn't take her to the vet straight away, I seemed to remember my last dog did this a little when he was a pup and it didn't last long and fizzled out when I put bitter aloes on it. Whenever I put anything on this - aloe vera gel, water, malaseb shampoo, non-toxic soothing ointment she always just started licking - so I have left it well alone. 

Then I found the hair loss (it's not completely bald - but very thin and no way I could show her like that) extended slightly up that leg and then saw a patch under her sternum - just a slightly redder/pinker patch of skin - which I don't see how she would be able to reach with her head - making me think it couldn't be psychological after all.

She does sometimes turn round and nibble herself in random places on her body very suddenly as though something is irritating her, but she was flea treated with frontline combo a short time ago and when I comb through I can find no evidence of anything on her or in her bedding and we have noticed nothing around the house either....and I have to avoid ivermectin products with her due to her being a collie.

Obviously I'm concerned that she/her skin might be irritated as those areas of skin look a little thicker and have an almost grubby appearance compared to the rest of her skin and despite her having had a bath - so am first wondering what it could be if not psychological, but I'm also wondering how long it would take for the fur to grow back as obviously I had really been looking forward to getting out to shows with her.

I want to take her to the vet - but we are so close to cracking the car issue, I don't want to ruin it by rushing - we've only just started turning on the car engine and the vets is too far to walk.....

so anyone else had a similar experience, we're only a month from her turning 6 months and I really want her to be comfy and for us to be able to get out to a few little shows.

If she has a few little itchy patches appearing, maybe its an allergy to something? 

I did consider that, but I changed her food from Royal Canin to a hypo-allergenic gluten free food. She was fine when she came to me - she grew up on a farm and here we don't have grass or many plants, though she's in contact with grass when on walks.

I've struggled to think what else she could be allergic to? Although I guess she could develop an allergy for something she was previously fine with?

I'm thinking allergy too. My last dog just scratched and scratched from quite a young age. Flea treated, still scratched. In the end I looked at what I was feeding her and read up about additives and colourants affecting dogs so changed her onto a food that was free from those things. In those days there wasn't a lot of choice, so I fed her Burns and she stopped scratching. Dog foods these days are much, much better,but there could be something in there that is causing this. Worth looking into as a starting point.

Oops I was writing my post and didn't see your post until after I had posted. Food seems unlikely now.

This is what she's on at the moment:

Fresh Scottish Salmon ( 45.8%), salmon meal (min. 14.1%), sweet potato( 10.7%),
potato flakes( 10.7%), salmon oil ( 8.77%),  vitamins and minerals( 1.30%), pea fibre( 4.16%), Lucerne ( 1.91%),  salmon gravy( 1.52%),dried apple (0.04%),  carrot flakes(0.04%), spinach flakes(0.04%), lovage powder(0.04%), seaweed meal(0.04%), dried cranberry(0.04%), aniseed and fenugreek(0.04%), mixed herbs (thyme, marjoram, oregano, parsley, sage) =(0.04%), glucosamine (min. 178 mg/kg), MSM (min. 178 mg/kg), chondroitin sulphate (min. 125 mg/kg),=(0.04%) camomile powder(0.01%), burdock root powder(0.01%), peppermint(0.01%), dandelion herb(0.01%)

This is what she was on until about 10 days ago:

Duck meal (min. 32.4%), trout (min. 21.9%), sweet potato, potato flakes, duck fat (min. 4.1%), pea fibre, duck gravy (min. 1.6%), salmon oil, vitamins and
minerals, Joint care pack (glucosamine (min. 0.01%), methylsulfonylmethane (min. 0.01%), chondroitin sulphate (min. 0.01%), dried apple, carrot flakes, lovage powder, seaweed meal, dried cranberry, aniseed and fenugreek, mixed herbs (thyme, marjoram, oregano, parsley, sage), camomile powder, burdock root powder, peppermint, dandelion herb

I guess if she was allergic to salmon/sweet potato/potato/pea fibre/apple/carrot/lovage/seaweed/camomile/burdock/dandelion/mixed herbs - they are in both foods ??? Obviously the Royal Canin she was on before had all manner of other potentially allergenic substances - like maize etc....

Could she be allergic to your washing powder or carpet cleaner?

We don't use carpet cleaner per say - and washing liquid is non bio liquitabs and I usually add a scoop of oxiaction powder as I wash at lower temps.

Could she have some sort of mite that I might not be able to see?

You could consider demodex.

Allergies can develop at any age. :(  I think if it continues or gets any worse, I'd ask the Vet for an allergy test, just incase it is something in the food.