What causes your arm to swell and go numb after injection?

Arm swelling and numbness after an injection can occur due to several factors, including localized inflammation, swelling from the injection itself, or nerve irritation or damage. If a needle hits a nerve or if there's excessive pressure from swelling, numbness can ensue. Allergic reactions or infections at the injection site may also contribute to these symptoms. If symptoms persist or worsen, it's important to seek medical advice.