Injectable products may contain unknown substances or contaminants.

(HealthDay)—Injectable skin-lightening products are potentially unsafe and ineffective, the U.S. Food and Drug Administration warns.

The agency has not approved any of these , and they may contain unknown or contaminants.

"These products pose a potentially significant safety risk to consumers. You're essentially injecting an unknown substance into your body—you don't know what it contains or how it was made," FDA pharmacist In Kim said Tuesday in an agency news release.

Not only do the products themselves pose risks, improper or unsafe injection methods can transmit disease, cause infection and lead to serious injury, according to the FDA.

Injectable skin-lightening or -whitening products claim to lighten the skin, correct uneven skin tone and clear up blemishes. Some even claim to treat conditions such as liver disorders and Parkinson's disease, the FDA pointed out.

The agency said the products—marketed for injection into a vein, a muscle, or under the skin—are sold online and in some retail stores and health spas. Some products have continued to be offered for sale even after being recalled as , the FDA said.

"In general, consumers should be cautious of any product marketed online with exaggerated claims on safety and effectiveness," Kim said. "They also should consult their health care practitioner before deciding to use any new product."

If you have side effects after using an injectable skin-lightening product, you should seek medical help as soon as possible, the FDA said. To report problems, call the FDA at 1-800-FDA-1088 or go to the agency's website.

Injectable skin lighteners aren't the only products of concern to the FDA. The agency said that noninjectable over-the-counter skin-bleaching products can pose safety risks, too.

More information: The American Academy of Dermatology offers skin health tips.