BACKGROUND: The Centers for Disease Control and Prevention state that a severe or immediate allergic reaction to the first dose of an mRNA COVID-19 vaccine is a contraindication for the second dose. OBJECTIVE: To assess outcomes associated with excipient skin testing after a reported allergic reaction to the first dose of mRNA COVID-19 vaccine. METHODS: We identified a consecutive sample of patients with reported allergic reactions after the first dose of mRNA COVID-19 vaccine who underwent allergy assessment with skin testing to polyethylene glycol (PEG) and, when appropriate, polysorbate 80. Skin testing results in conjunction with clinical phenotyping of the first-dose mRNA COVID-19 vaccine reaction guided second-dose vaccination recommendation. Second-dose mRNA COVID-19 vaccine reactions were assessed. RESULTS: Eighty patients with reported first-dose mRNA COVID-19 vaccine allergic reactions (n = 65; 81% immediate onset) underwent excipient skin testing. Of those, 14 (18%) had positive skin tests to PEG (n = 5) and/or polysorbate 80 (n = 12). Skin testing result did not affect tolerance of the second dose in patients with immediate or delayed reactions. Of the 70 patients who received the second mRNA COVID-19 vaccine dose (88%), 62 had either no reaction or a mild reaction managed with antihistamines (89%), but 2 patients required epinephrine treatment. Three patients with positive PEG-3350 intradermal (methylprednisolone) testing tolerated second-dose mRNA COVID-19 vaccination. Refresh Tears caused nonspecific skin irritation. CONCLUSIONS: Most individuals with a reported allergic reaction to the first dose of mRNA COVID-19 vaccines, regardless of skin test result, received the second dose safely. More data are needed on the value of skin prick testing to PEG (MiraLAX) in evaluating patients with mRNA COVID-19 vaccine anaphylaxis. Refresh Tears should not be used for skin testing.