Millions of Americans may have purchased counterfeit products online without ever realizing they bought a fake.

A new report from the Government Accountability Office (GAO) reveals that the rise of e-commerce is changing the market for counterfeit goods — and these ripoff items may be putting your health and safety at risk.

Warning: Counterfeit products sold on Amazon, Walmart and other popular sites

No longer are counterfeits obvious fakes, found mostly at flea markets and sold drastically below the retail price.

Consumers may have difficulty spotting a fake because the counterfeits appear more authentic, are nearly the same price as genuine goods and can be purchased from third-party sellers on reputable online retail websites.

Federal investigators bought 47 items from third-party sellers on popular consumer websites and 20 were counterfeit.

The report stated that the government agency purchased at least one counterfeit item and one authentic item from each of the five sites: Amazon.com, Walmart.com, Sears Marketplace, Newegg.com and eBay.com.

The items purchased were Nike Air Jordan shoes, Yeti travel mugs, Urban Decay cosmetics and UL–certified phone chargers.

All 13 of the Urban Decay cosmetics, six Yeti travel mugs and one UL-certified phone charger were found to be counterfeit. All 15 of the Nike Air Jordan shoes were authentic.

From higher levels of dangerous chemicals to an increased risk of electrocution, the health dangers associated with counterfeit goods can be frightening — they are inferior products.

Here are a few examples of the counterfeit items and the red flags to know about:

Misspelled label on counterfeit travel mug

Discrepancies in color, composition and package design

Missing key elements or certification markings

Protect yourself from buying counterfeit goods

The 47 items were purchased from third-party sellers. Protect yourself by buying directly from the manufacturer or its authorized retailers.

You can also check to see if the seller provides a mailing address or phone number, real-time customer service, customer reviews and third-party accreditation that can be verified.

And if you suspect that you’ve bought a counterfeit product, notify the brand owner and contact the place of purchase for a refund.