Sons asthma worsening

I recently had to take my 5 year old son to the doctors as I could see he was building up towards an attack. His blue inhaler was becoming ineffective and I couldn't control his asthma symptons. I was so disappointed as he had gone a year without needing his blue inhaler and I was hoping he was growing out of his asthma. He has been put on a course of soluble steroids which do seem to be doing the trick. The thing is, normally his trigger has been a cold, every single time, but there has been no cold or virus recently. The only thing that I can think of may be completely irrelevant. We have just been on holiday, where we stayed in a cottage. By day 2 George was wheezy and by week 2 he was having breathing difficulties (breathing fast, pulling in etc). It may be a complete coincidence but does anyone have any clue as to whether this could have contributed to his symptons? Dogs were allowed in this cottage but Georges grandma has a dog and this has never affected him before. I am so worried about where this may lead to as I have heard steroids are not a good thing to be on.

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i always look on that steriods have saved my kids and my lives after having bad attacks of our asthma they are different to the steriods that lets say athletes use ( i don't want to offend so this is general wording) please don't think of them as bad cos they arn't they are there and prescribed to hep u/child