Not so long ago corporate America dismissed environmentally conscious consumers as hemp-wearing hippies with too little buying power to demand much attention.

Now big brands are discovering it pays to go green. In the past six weeks alone Apple Inc. launched "A Greener Apple" campaign and pledged to remove toxic chemicals from its new computer products. Home Depot Inc. unveiled an Eco-Options stamp for more than 2,500 environmentally friendly products in its stores. The NBC soap opera "Days of Our Lives" staged a green wedding, complete with soy candles and a hemp suit for the groom. And Kohl's Corp. said it plans to convert most of its California stores to solar power.

Helping the movement along is a new breed of eco-celebrity keen on making environmental causes chic. Leonardo DiCaprio has his own eco site, and Madonna composed an eco-song for this summer's celebrity-packed "Live Earth" concert. Meryl Streep guest edited The Green Guide magazine. And when Oprah deemed "Going Green" worthy of a show in April, it became official: The environmental renaissance could no longer be ignored.

"It's now sexy to be green," said Bonnie Carlson, president of Promotion Marketing Association, a New York-based trade group. "It's very fashionable for consumers to say they're doing something to help the environment."

Yet, as the green movement grows, so does the confusion.

Few labeling standards exist to tell consumers which products are really helping the environment. Terms such as "green," "natural," "environmentally friendly" and "earth smart" don't mean much on their own. Even the definition of biodegradable -- which implies a product breaks down and returns to nature -- is in dispute. Does it take a year or many decades for a product to decompose? It is hard to tell from the label.

"This is a very old marketing tactic," said Dan Howard, chair of the marketing department at Southern Methodist University in Texas, who studies advertising and consumer behavior. "You take a look at whatever is perceived as favorable in society and try to associate your brand with it. It doesn't matter whether it makes sense or not."

More and more companies are carving out a separate budget for green marketing, just as many advertisers do for cause-related marketing or online ads.

The number of green product introductions skyrocketed between 2000 and 2005, according to the latest "green living" report from Mintel International Group, a Chicago-based market research firm. Household product debuts went from none in 2000 to 153 in 2005, new personal care products soared from 17 to 207 and food and drink product introductions jumped from 83 to 228.

The report, issued last September, concluded that "the entire green space is ripe for branding efforts." It also warned that the lack of labeling standards is confusing consumers, leading to a debate over what constitutes legitimate eco-branding and what is greenwashing, or the practice of projecting a green image without actually being green.

"It took 20 years to get organic standards put into place after the government said let's do this. And it's still not clear-cut," said David Lockwood, research director at Mintel. "Even if everybody's being honest, it's not that easy."

For example, a T-shirt can claim to be made of organic cotton when on close inspection only 5 percent of its content is organic. Likewise, skin care products can tout natural ingredients and still contain plenty of chemicals.

Aveeno, a skin care line from Johnson & Johnson, built its ad campaign around the "science of active naturals," ingredients including soy, oats and shiitake mushrooms. But critics say many Aveeno products also contain ingredients that are not natural. Cadbury Schweppes pledged to battle climate change by reducing carbon dioxide emissions, yet promoted its 7Up soda as "100 percent natural," a claim critics say is unfounded since the soda contains high-fructose corn syrup, a processed sweetener.

And Target Corp., purveyor of organic food and clothing, has come under attack from consumer groups for selling toys, shower curtains and other products that contain polyvinyl chloride, or PVC, a type of plastic that has raised health concerns.

An Aveeno spokeswoman said the business "has a long history of using natural ingredients tracing back to the brand's first product in 1945" and that the company "remains committed" to developing skin care products with natural ingredients.

Cadbury Schweppes responded to criticism in January by saying it would change its label to specifically highlight those natural ingredients "for which there is no debate," namely natural flavors as well as no added colors, no artificial preservatives and no caffeine.

Target said in a statement that the company is "intensively assessing our use of PVC and the viability of alternatives and actively pursuing opportunities, in collaboration with our vendors, to reduce PVC in our products and packaging."

Efforts are under way to help consumers navigate the onslaught of green marketing claims. Natural Home magazine is making a "huge push" over the next year to educate readers on determining what's green and what's not, starting with its July issue, said editor Robyn Griggs Lawrence.

The Consumers Union routinely updates its Web site, describing which labels are backed by third-party standards and which are generally meaningless claims. also keeps tabs on companies' green claims.