What Is Inside Those Disposable Diapers?

by Juliet Spurrier, MD and Nikki Beinstein Strait
Monday October 21, 2013 1:00pm
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Your baby is going to spend a lot of time in diapers so it makes sense to consider the materials they are made of. Are the materials really safe? Are all disposable diapers built the same? In this article we'll try to answer those questions.
This article is part of our review: Battle for the Best Disposable Diapers

Disposable diapers have become a great convenience in the modern world, but many parents question how safe the materials that constitute disposable diapers actually are. One might think that the reason the first disposable diaper was invented was to increase mobility among families, but that wasn’t the case. Disposable diapers were developed by Marion Donovan after World War II because of a cotton shortage. It wasn’t long, however, before mothers realized the practical benefits of Donovan’s 1950 diaper design: a rectangular plastic covering (initially from shower curtains) over layers of tissue paper.

Since then, disposable diapers have gone through many changes, including more than 1,000 patents filed in their name. Disposable diapers increased in popularity following the introduction of Super Absorbent Polymers in diapers in the mid-80's (more on this below). Today, an estimated 90% of US parents use disposable diapers, much to the chagrin of environmental activists who consider the landfill impact unethical.

Most recently, diaper manufacturers have responded to environmental and health concerns raised by many parents. There is a trend toward greener and more biodegradable disposable diapers, which we view as a step in the right direction. However, we're not out of the woods yet, and depending on which brand of diaper you choose, the risks and impacts vary. To understand the risks, however, we first need to break down the components of disposable diapers into their many parts.
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Diapers are constructed in three layers, an inner layer that sits against baby's skin is designed to be soft, stay relatively dry, and wick away moisture into the core. The absorbent core is designed to pull moisture in and trap it to keep wetness away from baby to avoid rashes. The outer layer is waterproof to prevent leaks.
Credit: BabyGearLab Staff
We urge parents to consider the materials used in each component of a diaper, and to demand transparent disclosure by diaper manufacturers. A summary of the basic layer components is provided below, but more interested parties will want to check out this article on Made How.
  • Inner Layer or Top Sheet - this layer sits next to your baby's skin and thus is the front line on any toxicity or materials risk issue. This material is key. Require your diaper provider to disclose what their inner layer is made of.
  • Absorbent Core - the theory is that this layer absorbs fluids, but the reality is that when baby repositions, fluid may be squeezed out of the core (potentially contaminated by the core materials) and back onto baby's skin. To enhance absorbency, every one of the diapers we tested includes a matrix of fluff material and chemical crystals known as Super Absorbent Polymer (SAP) to soak up and trap fluid (more on this below). The role of the fluff, usually made from wood pulp and may also include wheat/corn based materials, is to distribute the fluid, while the SAP is intended to absorb fluid and locks it in the core away from baby. The bulk of the diaper, especially when wet, is composed of the core materials. We consider this the 2nd most important material to understand.
  • Waterproof Outer Shell - all disposable diapers include some kind of waterproof material for the diaper's outer shell. These materials are most often some kind of petroleum-based plastic or plastic-treated material. Some green diaper companies use a plant-based plastic (aka bioplastic) to provide the waterproof coating, which you may see referred to as PLA or polylactic acid in their ingredients.

Manufacturers are increasingly aware of parents concerns about toxic materials, and thus many will list on their website and/or packaging what potentially harmful chemicals are not included. We've researched each brand of diaper in our Battle for the Best Disposable Diapers and attempted to list out what materials are explicitly noted as not included in that review.

Arrgh! The Mystery Ingredient May Be Toxic
Vexing to us is the lack of disclosure by many manufacturers about what, exactly, is in the diaper which they expect parents to place on baby's skin 24 x 7 for the next 3-5 years. We urge you to buy from manufacturers who offer complete transparency in their diaper ingredients. It is safer to buy from manufacturers who are not afraid to disclose their ingredients. The biggest brands, Huggies and Pampers, are often considered the most guilty on this score, but are far from the only manufacturers limiting their disclosure of materials. Some of this lack of disclosure is supported by our government, such as in the case of Fragrance ingredients, which can be considered a proprietary trade secret and exempt from detailed disclosure. As reported in the Huffington Post and elsewhere, "…due to the 'trade secret' status of fragrances, manufacturers are still not required by the FDA to disclose their ingredients on the label or in any other way." As a result, a manufacturer may bury dozens of potentially toxic chemicals under a "Fragrance" ingredient listing. For this reason, and others (see below on Perfumes), we urge parents to only buy Fragrance-free diapers.

The fact is that there are several potentially harmful chemicals that are known to be present in some disposable diapers, including: chlorine, dyes, fragrances, phthalates, and more. We advise relying on the Skeptic's Rule of Thumb when it comes to potentially harmful ingredients:
If they don't say it's not in there, then assume it's in there.
Unless a manufacturer explicitly assures you that their diaper does not include a potentially harmful ingredient known to be commonly used in diaper manufacturing, we advise you to assume they do. To simplify the process, we've attempted to compile a list of material disclosures in our Disposable Diaper review.

Super Absorbent Polymer (SAP)
The secret sauce inside disposable diapers since the mid-80's has been Super Absorbent Polymer (SAP). Referred to by various names such as hydrogel, sodium polyacrylate, polyacrylate absorbents, or in Pamper's FAQ as Absorbent Gel Material (AGM), these tiny crystals are carefully sprinkled inside the layers of the absorbent core of a diaper for their incredible ability to absorb and trap fluid (i.e. from urine and wet poopy). And it's not just major brand-names like Pampers and Huggies that use SAP, it is used in every one of the 20 diapers we tested, green disposable diapers as well as all the others.
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SAP is claimed to absorb up to 300x its weight in water and retain it. In the left photo, you see a small pile of white SAP crystals from a diaper's absorbent core. It has a consistency of a very fine white sand. We then added 65 drops of water, which was completely absorbed by the SAP in a few minutes to become the gelatinous crystal pile you see from two angles in the center and right photos.
Credit: BabyGearLab Staff
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This photo shows the same brand diaper (Bambo), cut in half to reveal the absorbent core, when dry (top) and when wet after an overnight wetting (below). The top layer of the wet diaper feels dry to the touch, owing to the urine being effectively absorbed into the core. SAP crystals do the heavy lifting, and are sandwiched between the upper and lower layers of the diaper core material.
Credit: BabyGearLab Staff
Concerns about SAP are often cited and come from multiple perspectives.
  • First off, SAP is a relatively new material, having been invented in Japan in the early 70's and only used in diapers since the mid-80's.
  • It is unclear if sufficient testing has been done to assure that SAP is non-toxic and safe.
  • Most SAP in use today is derived from petroleum, and thus may contain chemical components of concern
  • SAP was linked with Toxic Shock Syndrome (however, it appears that SAP itself was not a direct cause; more on this below).

In our own research, we have not been able to find credible evidence-based studies which prove that SAP is either toxic or dangerous to humans. And, to the contrary, we have found a number of presumably tree-hugging green diaper companies who have concluded that the SAP they use is safe and non-toxic including but not limited to:
  • Bambo
  • The Honest Company
  • Seventh Generation

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Super Absorbent Polymer (SAP). While believed to be safe and non-toxic, this crystal-like gel material freaks out many-a-parent if it escapes from a soaked diaper's absorbent core and onto baby's skin. Manufacturers recommend just wiping it off.
Credit: BabyGearLab Staff

On the whole we're left concluding, albeit somewhat anxiously, that the body of evidence (and lack thereof to the contrary) suggests that SAP appears to be safe. Perhaps as a testament to the apparent safety of SAP, our founder and one of the primary authors of this article, Dr. Juliet Spurrier, is using Bambo Nature diapers, which are a green diaper with SAP, for overnight diapers with her children (although Dr. Spurrier notes, emphatically, that if she knew then what she knows now about disposable diapers, she would have chosen cloth diapering for daytime use, but still used a green disposable for overnight).

This short video will give you a feeling for SAP's unique water absorption capabilities:

Link to Toxic Shock Syndrome
SAP has been linked to Toxic Shock Syndrome (TSS). However, most experts do not believe the SAP itself was the cause, but rather the prolonged internal-use which SAP tampons enabled, which provided a breeding ground for bacteria. In 1978 Proctor & Gamble introduced the ill-fated Rely tampon. The use of SAP allowed the Rely tampon to absorb an entire menstrual flow, allowing it to be used for a prolonged period without replacement. By 1980, the popular Rely tampon was linked to an uptick in Toxic Shock Syndrome incidence and was recalled. The prolonged internal-use the Rely tampon encouraged is believed to have created an increased opportunity for growth of bacterium and thus increasing risk of TSS infection. The use of SAP in tampons was subsequently discontinued.

Biodegradable SAP
SAP is a plastic and most, if not practically all, of the SAP in diapers today is derived from petroleum. However, recently several companies are manufacturing SAP produced from plant-based bio-plastics. Similar to the processes used for creating bio-degradable trash bags, a combination of cellulose from wood or wheat, and starch from corn, potato, yams or other starch-rich plants, can be used to make a plant-based SAP which has similar absorbency but improved biodegradability. These materials are relatively new, and thus have not undergone as significant testing as petroleum-based SAP. However, the use of natural and sustainable materials and increased biodegradability are a virtuous combination. While many green diaper companies utilize plant-based core materials derived from wood/wheat/corn, it us unclear to us whether any are actually using plant-based SAP instead of petroleum-based SAP.

Chlorine-free and Why It Matters
In disposable diapers, chlorine is used as a bleach to whiten diaper material. The problem with chlorine is that it emits small traces of known toxic chemicals called dioxins during the bleaching process. The desire to keep baby from being exposed to dioxins is the primary motivation for using chlorine-free diapers.

Based on animal studies, dioxins are believed to have the ability to “cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer.” The Environmental Protection Agency has identified dioxins as a “likely human carcinogen.”

While dioxins are only left in trace quantities in chlorine-bleached diapers, we prefer "none" to "trace" when it comes to babies. That's why we advocate going with a chlorine-free diaper. Happily, going chlorine-free does not need to pinch your pocketbook; our Best Value award winner, the Target Up & Up diaper is both low-cost and chlorine-free.

Perfume-free Preferred
Perfume fragrances are sometimes used in disposable diapers, presumably to mask poop's distinctive stench. However, an infant's rapidly evolving organ systems are both immature and exquisitely sensitive to chemical insults. The scents found in many diapers are strong and chemical-laden, harboring unnecessary irritants with potential to cause such health issues as diaper rash and respiratory symptoms. Equally concerning, manufacturers are not required to disclose the chemicals used in fragrances as the FDA allows them to consider their fragrances “trade secrets.” Organizations such as the Campaign for Safe Cosmetics have commissioned independent labs to examine fragrances and have found potentially dangerous synthetic chemicals in use.

Our recommendation is simple: choose a perfume-free diaper. You don't need it, and it's not worth the risk. And, like avoiding chlorine in diapers, avoiding perfume in diapers is easy and painless. A lot of great diapers are perfume-free, including the economic Target Up & Up diaper and most green diapers.

Be Careful About Dyes
Dyes are may be added to diapers to color them and/or create wetness indicators. These dyes can be a cause of skin rash, as they may cause allergic reactions in some babies. In a study published in Pediatrics in 2005, switching to dye-free diapers was shown to eliminate skin rashes which occurred in areas exposed to colored portions of diapers.

Some manufacturers have chosen to provide dye-free diapers. Top performing dye free diapers in our test include:
Other diaper companies, like Bambo and Honest Diapers, use dye pigments that do not contain heavy metals, which they believe are safe and hypoallergenic.

Our take on it: we like dye-free and recommend it. Features like wetness indicators though helpful are unnecessary and we'd prefer to keep it simple.

Fear of Phthalates
If you already read our article, Are Plastics Safe for Baby Bottles, you may know that phthalates are a plastic ingredient of concern in baby bottles. But, they may also be in your baby's diaper. Phthalates are mainly plasticizers, or “substances added to plastics to increase their flexibility, transparency, durability and longevity.” They are generally used to soften plastic, for example in making a soft vinyl, and are also commonly added to lotions and shampoos. In some disposable diapers, phthalates may be used as part of the process to create a waterproof outer liner. Phthalates are not tightly chemically-bonded to the plastic, and as noted in the Pediatrics paper cited below, "are therefore continuously released into the air or through leaching into liquids."

Phthalates are on the radar of the medical community — and we think they should be on yours too — due to potential toxic effects to the developing endocrine and reproductive systems, to which infants are particularly vulnerable. Phthalate sources are not limited to some diaper liners, but a broad range of "plastic products such as children's toys, lubricants, infant care products, chemical stabilizers in cosmetics, personal care products, and polyvinyl chloride tubing." The American Acadamy of Pediatrics journal, Pediatrics, pubished a paper titled, Baby Care Products: Possible Sources of Phthalate Exposure in July 2008. In it they noted, "Children are uniquely vulnerable to phthalate exposures given their hand-to-mouth behaviors, floor play, and developing nervous and reproductive systems."

Not all diapers use Phthalates. But, figuring out which ones do is a challenge, since US law does not currently require disclosure of Phthalates.

Again, we advocate using the Skeptic's Rule of Thumb when it comes to potentially toxic ingredients: "if they don't say it's not in there, then assume it's in there." Here's a few manufacturers who have gone on record stating there are no phthalates in their diapers:
Environmental Impacts
The Sierra Club has a balanced view on disposable diapers, and they encourage the use of biodegradable diapers if you use disposables.
The largest independent study to date, released in 2008 by Britain’s Environment Agency, found that the overall impact of cloth versus disposable diapers is highly dependent on how you wash and dry your cloth diapers. For example, if you wash cloth diapers in a full load with water at or below 140 degrees Fahrenheit, line dry the diapers, and reuse them for a second child you would be reducing your global warming impact by 40%. However, if you use a dryer for the diapers and use water above 140 degrees, your impact could be 75% worse than using just disposable diapers. (Source: Sierra Club Green Home)

Our recommendation is to consider the level of biodegradability in your decision making. Unfortunately, our favorite green diapers are only partially biodegradable. Here's some diapers to take a close look at:
  • Broody Chick is the only one of 20 diapers we tested that claims 100% biodegradability. Unfortunately, this very green diaper did not score very highly in our performance ratings.
  • Bambo Nature claims 80% biodegradability, and was also the highest scoring diaper in our performance ratings.
  • Attitude offers a biodegradable inner shell and padding, and was the 2nd highest scoring diaper in our performance tests.
  • Natural Babycare offers a biodegradeable back sheet film based on corn and biodegradable high loft for their core.

Our Recommendations
Our advice is simple: play it safe with your baby.

Although it is difficult to know exactly how much these chemicals from disposable diapers can affect your baby or to what degree your risk of exposure to them is, we’d say it’s better to be safe than sorry. Based on the research compiled above, we recommend you choose a diaper with the following characteristics:
  • Chlorine-free
  • Fragrance-free
  • Phthalate-free preferred
  • Dye-free (or at least pigments without heavy metals)
  • A high level of biodegradability

No diaper we tested was perfect, but the top three performing diapers in our tests are all good options from our point of view and we'd recommend you give them a close look:
To learn more about’s in-depth Review of 20 Disposable Diapers, which includes a listing of the disclosed material contents of each diaper, go to:

  Article Views: 41,741
Juliet Spurrier, MD
About the Author
Dr. Juliet Baciocco Spurrier is a board certified pediatrician, mother of two, and founder of BabyGearLab. Juliet earned her Bachelor of Arts degrees in Anthropology and Italian Literature from the University of California at Berkeley and her Medical degree from Georgetown University School of Medicine in Washington DC. She completed her pediatric residency at the Doernbecher Children's Hospital at Oregon Health & Science University in Portland, OR, and subsequently practiced pediatrics in both the Pacific Northwest and Silicon Valley. Juliet serves as Mom-in-Chief at BabyGearLab, where she oversees all baby product review activity, assuring that each review delivers on our commitment to quality.

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Evienne · Metairie, LA  Aug 21, 2013
10:28pm PT
I am so indebted to you, Doctor, for all the excellent research and obvious care that went in to writing this article.I have bought the Bambo diapers for my grandchild,as you suggested, and find that they are superior to the others.
I would appreciate an update from you on the new Bambo diapers, as I have read some unfavorable reviews on Amazon. Could you test the new ones ? Thanks.
kcm1535   Sep 26, 2013
03:32pm PT
I second the request to please test the new Bambo diapers. Thanks.
naturalmom · NJ  Dec 3, 2013
10:54am PT
Thanks so much for your meticulous research! I found this article to be tremendously informative, yet I am still no closer to making a decision between cloth and disposable =(
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