If sensitive, the ears should have shown it earlier and not wait so long actually. U need to practice good hygiene for the ear rings, take them out everyday and wash them w soap, ensure ur LO ears are washed too - the back of the ears - it could be the surrounding not clean
If really sensitive, some pole go for gold ear rings, u can try gold plated or platinum or stainless steel - these have low reactivity for the ears
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