We have previously reported on injuries suffered by young children exposed to methacrylic acid-containing nail primers and the need for public education efforts concerning this potential household hazard. However, some primers contain alternative ingredients, which may or may not pose the same risk; product labeling information is variable and may be confusing to consumers.To investigate the relationship between pH of different primer products, product contents, and appropriateness of product labeling and packaging.Twenty-three commercially available primers were grouped by product contents: (methacrylic acid vs others). Product pH was measured and product labels were scored on 7 warning points: "poison and/or corrosive," a "caution to avoid contact and/or to use a barrier when handling the product," a "skin first aid," and "eye first aid," an "ingestion first aid," a caution to "keep out of reach of children," and a "in emergency, contact a poison center." A summative "global hazard notification score" was calculated for each product. Data were analyzed using correlations and the two-sample t-test.None of 23 products tested were contained in a child-resistant container and none included all 7 label items. Product pH ranged from 1.90-8.55 (mean pH 4.59 +/- 1.99); 20 products had pH < 7.0. Only 1 product advised, in the event of a poisoning, that a poison center be contacted. Of 20 acidic products, only 7 alerted users that the contents could cause burns. The mean global hazard notification score (MAX = 7) was 3.6; global hazard notification score did not correlate with pH. Methacrylic acid-containing products had a lower pH (mean 3.43 +/- 0.78) than those without methacrylic acid (mean 5.34 +/- 2.18), p = 0.008. When the primer bottle was separated from the rest of the packaging which comprised the artificial nail "kit," 50% of products lost all of their warning information.Most, but not all, artificial nail primers analyzed in this study were highly acidic. Labeling and packaging of many nail primers are inadequate, given the potential of methacrylic acid in these products to cause burns and the toxicity of most nail primers. We agree with the Consumer Product Safety Commission's recently proposed rule to require cosmetic manufacturers to repackage methacrylic acid-containing household products in child-resistant containers. We also urge manufacturers to alert consumers to the hazards of nail primers by better labeling. Manufacturers should also investigate the feasibility of either substituting other chemicals or lowering the concentration of methacrylic acid.