Your dog’s coat should be checked everyday when you are with him/her. You might find that hair loss is one of the most common problem and so look for anything different including bald areas. The reasons associated with hair loss in a dog are many.
Hair loss is the clinical sign of alopecia, partial or complete.
Your dog might be biting and/or scratching to the extent that he/she is losing his/her hair. A way to stop him/her from doing so is to use a cone on his/her head, however it is best to try and find out the history of how your dog usually behaves, and establish when the biting and/or scratching started.
When the weather is getting warmer it is normal for your dog to usually lose some hair but there still shouldn’t be patches of hair falling out.
If the fur loss is unexpected, consult your veterinarian early so that some tests can be done to identify the exact reason, to prevent any sign of disease, to treat as appropriate, and so it can be monitored regardless how small it might be.