What are SAPs, and are they safe in disposable nappies?

July 13 2026, by Hello Charlie Blogs, 5 min reading time

Cut open a clean disposable nappy and you will find more than fluffy pulp. The tiny crystals mixed through the absorbent core are superabsorbent polymers, or SAPs. When wet, they swell into a gel and help keep liquid away from a baby’s skin.

Parents often discover SAPs after seeing a few clear gel beads during a nappy change—and naturally wonder whether something that expands so dramatically belongs next to their baby. Here is what the evidence actually tells us, without treating every synthetic material as dangerous or every manufacturer claim as proof.

Quick answer: SAPs used inside modern disposable nappies are generally considered safe for their intended use. They are large, cross-linked polymers designed to remain in the nappy core and are not readily absorbed through skin. Nappy fit, dryness, fragrance, lotions and how often the nappy is changed are usually more relevant to irritation.

What are disposable nappies made from?

Designs vary, but a modern disposable nappy usually contains:

a soft non-woven top sheet next to the skin;
an acquisition layer that distributes liquid;
an absorbent core made from cellulose fluff, SAP or both;
a water-resistant outer layer;
elastic, adhesives and fastening materials; and
sometimes fragrance, pigments or a lotion on the top sheet.

SAP lets manufacturers make a thinner nappy that can still retain a substantial amount of fluid. Once urine reaches the core, the polymer swells and holds the liquid in a gel network.

Does SAP touch a baby’s skin?

In normal use, dry SAP is enclosed within the core rather than sitting loose on the skin. Safety assessments consider whether small amounts of a material or impurity could move through the layers under realistic conditions. The polymer itself is too large to be readily absorbed through intact skin.

If a nappy is extremely full, torn or defective, you may see soft gel beads on the skin. Gently wipe them away, rinse if needed and change the nappy. Contact the manufacturer if leakage happens repeatedly.

Common SAP safety claims, checked

“SAP is toxic if swallowed”

Nappy-core SAP is not intended for eating, and a damaged nappy should be kept away from a child who mouths objects. However, the presence of sodium polyacrylate in another regulated application does not prove that nappy granules are food-grade, and a safety data sheet does not replace a finished-product assessment. If a child swallows a meaningful amount, call the Australian Poisons Information Centre on 13 11 26 for case-specific advice.

“SAP causes toxic shock syndrome”

This claim confuses nappies with a historic tampon-safety issue. Toxic shock syndrome involves bacterial toxins and particular conditions of internal tampon use. It is not evidence that the contained absorbent polymer in an external baby nappy causes the same condition.

“SAP causes asthma”

A small mouse study of emissions from disposable nappies has often been stretched into a claim about SAP. A nappy is a complex product, so an emission response cannot automatically be assigned to the polymer core. Fragrance and other volatile ingredients are a more plausible concern for a scent-sensitive household. Choose fragrance-free nappies if odour or respiratory sensitivity is an issue.

“SAP causes nappy rash”

Nappy rash is usually an irritant contact dermatitis driven by wetness, urine and faecal enzymes, friction and skin-barrier damage. Candida, diarrhoea, antibiotics and existing eczema can also contribute. By pulling liquid into the core, an effective nappy can help keep the surface drier. That does not mean every nappy suits every baby; added fragrance, lotion, dyes, fit and surface materials may still matter.

What the research says

Published quantitative risk assessments evaluate nappy materials using their toxicology, location in the product and potential transfer to skin. Reviews report that the main polymers used in disposable nappies are biologically inert and well tolerated under intended use.

Several of the most frequently cited papers include authors employed by nappy manufacturers. That does not invalidate the data, but it is a reason to read conclusions alongside methods, affiliations and the absence or presence of independent replication. The sensible conclusion is not “every disposable nappy is identical”; it is that there is no convincing evidence that properly contained SAP is a routine toxic exposure for babies.

SAPs and nappy rash prevention

The Royal Children’s Hospital advises that preventing and treating ordinary nappy rash centres on keeping skin clean and dry, changing nappies promptly and applying a thick barrier cream. The nappy should fit without rubbing or leaving deep marks.

Change a soiled nappy as soon as possible.
Clean gently with warm water and a soft cloth when skin is inflamed.
Pat or air dry; do not scrub.
Use a thick zinc oxide or petrolatum-based barrier.
Allow nappy-free time where practical.

Seek medical advice if a rash is severe, spreading, blistered, associated with fever, or not improving with simple care.

The real drawback: disposal

Conventional SAP is not readily biodegradable. It is mixed with cellulose, plastic and waste in a used nappy, making recovery difficult. A thinner nappy may use less material than an old-fashioned pulp-heavy design, but it still contributes to landfill.

When comparing “eco nappies”, look beyond one ingredient. Ask:

How much of the product is renewable or recycled?
Which parts are independently certified?
Is fragrance or lotion added?
Does a compostability claim apply to the whole nappy or one component?
Is the claimed disposal method actually available where you live?

For the broader chemistry and other uses of SAPs, see What Are Superabsorbent Polymers?. You can also explore Hello Charlie’s product-selection standards.

Sources and further reading

This article provides general information and does not replace medical advice.