If you look at the ingredient label of your favorite shampoo or laundry detergent, you'll likely see the word "fragrance" or "parfum." What you won't see is a list of the chemicals and other ingredients used to manufacture that synthetic scent. Product manufacturers don't have to tell you what's in their fragrances, as those ingredients are considered a trade secret and protected by law.

But scented products are everywhere — perfume, cologne, conditioner, moisturizer, deodorant, shaving cream, air freshener, makeup, floor cleaner, candles, you name it. Many of them are applied directly to the skin, and others will linger in the air you breathe, which is why consumers and environmental groups have been pushing for more transparency in the fragrance industry — an industry expected to be worth $43 billion worldwide within the next few years — as to what, exactly, is in their products.

Over the last few years, a handful of big companies have started to come clean. The latest one is Procter & Gamble, which recently announced that by the end of 2019, it will share all fragrance ingredients down to 0.01 percent for more than 2,000 of its products sold in the U.S. and Canada. This goes a step further than what the company already does, which is publish its "full fragrance palette" with a list of all the ingredients used. However, that list does not break down which ingredient are in which product and in which amount.

SC Johnson rolled out a product-specific ingredient list in 2015 for some of its Glade products, and the global manufacturer shares a list of more than 3,000 ingredients online. The Clorox Company shares its list of fragrance ingredients, Unilever announced a similar initiative that will be finished at the end of 2018, and Reckitt Benckiser says it will furnish such a list by 2020.

Providing this information to consumers is a big step in the right direction, but critics argue it doesn't go far enough. They say some of the ingredients should be removed because they pose a health risk to consumers.

How fragrance can affect your health

Scented candles If the candle you're burning contains a fragrance, then the chemicals in that fragrance are going into the air. Some people have allergic reactions when they breath in scented products. (Photo: Amanda Steed/Shutterstock)

We've known for some time that artificial fragrances can have a negative effect on the way we feel. Back in 1995, a study by Louisiana State University revealed that inhaling perfume from the strips in magazine advertisements could adversely affect asthma sufferers. More recently in 2016, a study of more than 1,100 American adults found that 34 percent of them had migraine headaches and trouble breathing when exposed to scented products. And about 15 percent of them reported having to miss a day or more of work due to fragrance exposure.

The FDA warns that certain fragrance ingredients can cause allergic reactions or sensitivities in some people, even if they're considered safe. But the FDA does not have legal authority to require allergen labeling for products such as cosmetics, so you won't see allergy warning labels on personal care products.

The most controversial ingredients

Man looking at bottle of cologne in bathroom Studies on diethyl phthalate, a common fragrance ingredient, suggest that, in animals, some phthalates damage sperm and affect male reproductive development. (Photo: Sjale/Shutterstock)

In 2010, the Campaign for Safe Cosmetics, a consumer advocacy organization, commissioned laboratory tests for 17 leading perfumes on the market. The Environmental Working Group (EWG), a nonprofit environmental organization, analyzed the data and found that those big-name scents contained 38 chemicals that were not listed on the ingredient labels. The average fragrance product tested contained 14 secret chemicals. "Among them are chemicals associated with hormone disruption and allergic reactions, and many substances that have not been assessed for safety in personal care products," the EWG reported.

One chemical in particular, diethyl phthalate or DEP, is especially worrisome. Phthalates are a group of chemicals used in hundreds of products, and DEP is commonly used in fragrance products, the U.S. Food and Drug Administration (FDA) says. The FDA says DEP "does not pose known risks for human health as it is currently used in cosmetics and fragrances."

However, the Consumer Product Safety Commission (CPSC), which did its own tests to evaluate DEP's toxicity, says DEP can be considered "toxic" under the Federal Hazardous Substances Act. The research found that DEP, when applied directly to the skin, did not cause any irritations in either animals or humans. But when it was taken orally, "DEP induced toxicity in a variety of organ systems such as the liver and kidney," the CPSC found.

In addition, previous studies on DEP in animals suggest that some phthalates damage sperm and affect male reproductive development.

Another concerning chemical is musk ketone, which is a synthetic version of the fragrant natural compounds produced by several types of animals and a few plant species, according to the American Chemical Society. It's a way to meet the demands for musk fragrance without sacrificing animals to make it. However, studies have shown this ingredient concentrates in human fat tissue and breast milk.

And lastly, according to a two-year study conducted by the National Toxicology Program, the fragrance compound myrcene has shown "clear evidence" of carcinogenic activity in rats.

The EWG says the FDA has not studied most fragrance chemicals for safety when used in spray-on products such as fragrances. Nor have most been evaluated by the safety review panel of the International Fragrance Association (IFRA), which has a list of 3,999 possible fragrance ingredients used in consumer products that meet the organization's safety standards. Of course, the companies that use synthetic fragrances in their products insist they are safe.

Lack of sufficient oversight

Woman shopping for perfume The FDA has not studied spray-on products such as fragrances for safety. (Photo: Miki Studio/Shutterstock)

Even if fragrance ingredients were reviewed for safety by the IFRA, many critics would question those findings because the IFRA is run by the fragrance industry, according to Women's Voices for the Earth (WVE), a national women's health nonprofit organization. The group asserts that "allowing the fragrance industry to self-regulate, and establish itself as the sole authority on fragrance safety, simply does not serve the public health interest."

WVE says that many studies on fragrance ingredients are commissioned by manufacturers, and those studies are not published, peer-reviewed or publicly available. They also assert that the most controversial ingredients, such as the ones mentioned above, haven't been studied by the IFRA's research group in the past 40 years.

Fragrance-free is no guarantee

Woman looking at laundry detergent bottle Choosing a product marked 'fragrance-free' doesn't mean it contains no fragrance ingredients. It means the product doesn't have an odor. (Photo: Gloriole/Shutterstock)

Given all of this, you may be tempted to go the fragrance-free route. Here's the thing, though: Fragrance-free doesn't mean a product is free of fragrance chemicals — it only means the product is free of odor, according to the University of Tennessee, Knoxville, Safety Office. The university reports that products must be marked "without perfume" to indicate no fragrance has been added.

In addition, a product labeled "unscented" may contain a masking fragrance, and if it does, that masking agent is not required to be on the ingredient label.

So while it's great news that leading manufacturers are acknowledging consumer concerns about the ingredients in fragrances and making those ingredient lists publicly available, clearly we still have a long way to go in terms of studying those ingredients to determine whether they're truly safe.

Angela Nelson ( @bostonangela ) is an exhausted mom of two young daughters and two old cats, and a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide.