Finally, any time your child ingests something that is not food, it can be helpful to contact the poison center that serves your area by calling 1-800-222-1222 (a nationwide number in the U.S. that routes your call based on your area code) for guidance.

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Symptoms can include difficulty breathing, vomiting and redness on the skin depending on how the affected person comes into contact with the poison.

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The people who initially came into contact with the letters showed no symptoms of exposure to the poison, but three officers who later examined the New York letter experienced minor symptoms that have since abated, police said.

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