A growing number of Americans are seeking so-called green cleaners -- products made with natural, nontoxic, and biodegradable ingredients. Sales of natural cleaning products totaled $105 million in the last year.

Some of these cleaners promise that they contain natural (instead of synthetic) agents, break down quickly in the environment, or pose less of a toxic threat to humans and ecosystems. But critics caution that just because the ingredients in green cleaners are plant-based or natural doesn't necessarily mean they're safe.

Although green cleaners may purport to list all ingredients, the market is largely unregulated -- which means consumers still must be wary of what's in the bottle. Even cleaning products labeled "natural" may contain some fraction of synthetic chemicals. Or they may contain natural ingredients consumers would rather avoid, such as petroleum distillates, some of which can cause cancer. And just because a cleaning product is biodegradable and made from plant-based sources doesn't mean that it is without potential adverse effects on health.

Plant-based ingredients included in some green cleaners include limonene (a citrus-based oil), pine oil, and the foaming agent coconut diethanolamide -- all of which can cause allergic dermatitis. And a recent study of natural and nontoxic consumer products found the suspected cancer-causing chemical 1,4-dioxane in roughly half of 100 tested products -- including several dishwashing liquids with words such as "Earth friendly" and "eco" in their brand names.

Consumer advocates have pressed for stricter labeling rules, but the industry has resisted, arguing that long lists of ingredients would create a distraction on product labels, drawing attention away from important safety information.