Apples are commonly coated with food-grade wax to extend their shelf lives.
Waxed apples aren't "known carcinogens"; the use of wax on apples isn't a secret.
In April 2016, the web site MetaSpoon published a blog post (titled: "He Pours Boiling Water On An Apple From The Grocery Store. Watch What Appears On The Skin... GROSS!") which held that the wax used to preserve fruits are riddled with pesticides:
Apples are so healthy and delicious, it really is no wonder that they’re such a popular snack. All you have to do is give them a quick wash and pack them, right? After watching this video, maybe not. Apparently, many producers will coat their apples with wax to help preserve the fruit. This is particularly true for apples found at grocery stores. Some experts say that wax is harmless, as it’s not digested by our system. But others argue that the real danger lies in the pesticide residue that the wax may have trapped in. Next time you buy apples, it might be worth finding out just how much wax coating there is. Want to get rid of the wax? Try scrubbing your apples in a bath of warm water, lemon juice, and baking soda!
The post linked to a January 2016 YouTube video, during which a person uses boiling water to remove the wax from apples. That person claimed waxed apples cause cancer:
Be Careful when eating apples. Please don't eat the skin of the apples because it's coated with wax. Check before you eat many of the fruits. Wax is being used for preservation purposes and cold storage. You might be surprised especially apples from USA and other parts are more than one year old, though it would look fresh. Becox wax is coated, preventing bacteria to enter. So it does not get dry. Please Eat Apples after removing the wax.
In the clip, the individual gave no information to substantiate the claim. He also noted that the apples "changed color" when exposed to boiling water, a procedure familiar to many viewers, and which is most commonly described as "cooking." (Apples are not the only fruits that darken in color when exposed to direct and sustained heat.)
The clip's initial fallacy hinged on the implication that wax on apples was a little-known secret. However, according to the Food and Drug Administration, waxed produce is widely, openly available and safe [PDF]:
Many vegetables and fruits make their own natural waxy coating. After harvest, fresh produce may be washed to clean off dirt and soil — but such washing also removes the natural wax. Therefore, waxes are applied to some produce to replace the natural waxes that are lost.
Wax coatings help retain moisture to maintain quality from farm to table ... Waxes also help inhibit mold growth, protect produce from bruising, prevent other physical damage and disease, and enhance appearance[.]
The Produce Marketing Association (an international trade group) reiterated the FDA's explanation of waxed apples and other produce items. The PMA also explained that the substances used are always subject to strict FDA scrutiny, and are safe to eat even when whitened due to exposure to extreme temperatures. That document outlined guidelines for use of wax on produce in general:
Many fresh fruits and vegetables make their own natural waxy coating to help retain moisture. Extensive washing at the packinghouse removes this natural wax, so waxes are applied to some produce items to replace the natural ones that are lost.
Each piece of waxed produce only has a drop or two of wax. Waxes may be mixed with water or other wetting agents to ensure they are applied thinly and evenly.
Waxes help retain the fruit's or vegetable's moisture during shipping and marketing. Waxes also help to inhibit mold growth, to protect fruits and vegetables from bruising, to prevent other physical damage and disease, and to enhance appearance. By protecting against moisture loss, wax coatings help fresh fruits and vegetables maintain wholesomeness and freshness.
Waxing does not improve the quality of any inferior fruit or vegetables; rather, waxing — along with proper handling — contributes to maintaining a healthful product ... Commodities that may have coatings applied include apples, avocados, bell peppers, cantaloupes, cucumbers, eggplants, grapefruits, lemons, limes, melons, oranges, parsnips, passion fruit, peaches, pineapples, pumpkins, rutabagas, squash, sweet potatoes, tomatoes, turnips, and yucca. However, they are not always waxed.
Waxes by themselves do not control decay; rather, they may be combined with some chemicals to prevent the growth of mold. The safety and use of these substances are strictly regulated by the U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency.
Coatings used on fruits and vegetables must meet the food additive regulations of the FDA. Extensive research by governmental and scientific authorities has shown that approved waxes are safe to eat. Waxes are indigestible, which means they go through the body without breaking down or being absorbed.
FDA requires wax labeling for fresh fruits and vegetables that have been treated with postharvest wax or resin coatings. Consumers will see signs in produce departments that read: “Coated with food-grade vegetable-, petroleum-, beeswax-, and/or shellac-based wax or resin, to maintain freshness” followed by a list of the commodity (-ies) coated with these waxes or resins). In today's marketplace, none of these coatings is animal-based, and they all come from natural sources.
Packaged fresh fruits and vegetables that have information on the label (such as the product name, weight or brand) must also be labeled for wax or resin coatings by the packer, repacker, or shipper.
The topic also was addressed by food safety experts at Best Food Facts. According to their analysis, not only do apples often produce their own wax (dependent on crop variables), but that an apple's natural wax contained a component that inhibits (not encourages) cancer cell growth:
Remember, apples are alive even after they are picked and will continue to live, provided they have the sufficient resources and an acceptable environment. The waxy coating produced by the apple and found on its skin protects it. The waxy coating can appear milky sometimes, but if you rub it gently, you can actually get it to it shine.
The natural wax on the fruit of the apple contains about fifty individual components belonging to at least half a dozen chemical groups. The major cyclic component of apple fruit wax is called ursolic acid and is highly water-repellent. Research has shown that ursolic acid is capable of inhibiting various types of cancer cells and can serve as a starting material for synthesis of more potent bioactive compounds such as antitumor agents.
Apples weren't always coated with additional wax, as they often are harvested with a natural coating of wax. However, all wax used on apples is subject to FDA guidelines for food safe additives, and none of the "waxed apples cause cancer" claims we found included a single known carcinogen commonly used in the process. Waxing apples is widely deemed both a safe and often natural occurrence, and the use of wax to coat apples is neither a secret nor credible health risk.
While there are some credible concerns about harmful pesticides caught in the wax used to coat apples and other fruits and vegetables, there are easy ways to avoid or minimize the risk of ingesting them. According to the National Pesticide Information Center, a collaborative effort between Oregon State University and the Environmental Protection Agency, most pesticide residues can be removed by rinsing fruits with water or scrubbing them with a soft brush. More information about what pesticides are in the food supply and how to avoid them can be found in this March 2015 report.
However, the overall risks of pesticide residue are quite low, even with conventionally grown produce, and since the Food Quality Protection Act was passed in 1996, very tightly regulated in the United States. However, wax on an apple is not a visual representation of trapped pesticides, nor is it an indication that any chemicals or toxic substances are present.