More than half the baby shampoo, lotion and other infant care products analyzed by a health advocacy group were found to contain trace amounts of two chemicals that are believed to cause cancer, the organization said yesterday.

Some of the biggest names on the market, including Johnson & Johnson Baby Shampoo and Baby Magic lotion, tested positive for 1,4-dioxane or formaldehyde, or both, the nonprofit Campaign for Safe Cosmetics reported.

The chemicals, which the Environmental Protection Agency has characterized as probable carcinogens, are not intentionally added to the products and are not listed among ingredients on labels. Instead, they appear to be byproducts of the manufacturing process. Formaldehyde is created when other chemicals in the product break down over time, while 1,4-dioxane is formed when foaming agents are combined with ethylene oxide or similar petrochemicals.

The organization tested 48 baby bath products such as bubble bath and shampoo. Of those, 32 contained trace amounts of 1,4-dioxane and 23 contained small amounts of formaldehyde. Seventeen tested positive for both chemicals.

"Our intention is not to alarm parents, but to inform parents that products that claim to be gentle and pure are contaminated with carcinogens, which is completely unnecessary," said Stacy Malkan, a spokeswoman for the Campaign for Safe Cosmetics, which is calling for the government to more strictly regulate personal care products such as shampoo, lotion and makeup.