Is it okay to use hair dye on my blonde patches every 5 weeks. (photo)

I've got blonde patches on the side of my head and when I get a haircut, (short on the sides) it's very noticeable so I dye ONLY the patches to match the rest of my brown hair. Is this harmful? I do it every 5 weeks. The photo will show how many patches there and and how short my hair is

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