Thank you for your question.
Calamine lotion is not recommended for dogs because the lotion often contains zinc oxide which can cause vomiting, diarrhea and gastointestinal upset if they lick or ingest it. So, if this is an area of skin irritation that your dog is licking or in a place he can reach, then its not the ideal product to use.
If your dog has a itchy patch, it is best to figure out what is causing it. If its a bacterial infection or a hotspot, it should be salt water bathed and probably covered with antibiotics (either systemic or topical). If its an allergic reaction, then you may want to settle his skin with an anti-histamine like Benedryl (HERE
If you are unsure of the reason for his itchiness, then you may want to consider having a vet evaluate it and help you treat this lesion appropriately.
I hope this information is helpful.
Please let me know if you have any further questions.
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