Chemistry of Diaper Wetness Indicator

Chemistry of Diaper Wetness Indicator

Previously, experienced mothers know by touching or smelling the diaper. It is not a wise thing to do. What can be the side effects if the diaper is not changed on time when wet? The result can be skin irritation and allergies.

So, it is important to change the diaper after a few absorbents. You can tell when the diaper needs to be changed by observing the diaper wetness indicator. 

Many disposable diaper brands offer this feature in their diapers. This indicator can tell about the diaper has reached its maximum limit of absorption, and it needs to be changed now. 

Types of Wetness Indicator

Wetness indicators are of two types;

  • the first one is Hot-Melt,
  • and the second one is a Ink Type.

Hot melt technology is adopted when the color of the wetness indicator changes from yellow to green or blue. On the other hand, ink type technology is adopted then the color fades and disappears. 

Diaper Indicator

Working Principle of Wetness Indicators

Hot melt wetness indicator type works by the combination of hot melt adhesive with such a substance that is color sensitive to pH value. The inner side of the back sheet contains this wetness indicator. The liquid is absorbed directly into the core and then moves to hot melt adhesives; it results in a change in pH value, and as a result, color is also changed. In this way, you can observe the wetness indicator. 

Keep one thing in mind that the transition interval ranges from 4 to 13, which means that neither strong acid nor strong alkali will cause a color change. It contains 1 to 3 stripes in the middle of the sheet. 

While in ink indicator, small molecule substances with color are mixed into the ink. When urine interacts with the mixture, a mixture of ink and color substance is washed away. In this way, the color disappears, and the purpose of the ink indicator is met. 


The adhesive used in the hot melt wetness indicator is polymer elastomer, such as SBS, SEPS, SIS, and SEBS. The widely used resins are phenyl ethylene and its segmented polymer SBS and SIS. A base resin that is used in the manufacturing of this indicator is pyroplasticity polymer elastomer. During the manufacturing, tacky resin, antioxygen, pH value indicator, and softener are used. 

On the other hand, ink wetness indicator is composed of modified acrylic resin, water, organic pigments, solvents, wax, additive solvents, and ammonia derivatives. 95% of the portion is taken up by the water, acrylic resin, and organic pigments. 

Characteristics of the adhesives used in the hot melt wetness indicator

  • Safe to use and reliable
  • Non-toxic
  • Thermo stability and environmental stability
  • Shows resistance to wash
  • Fast reaction time
  • Color changes sharply
  • Gradient function indicator that indicates a color change from yellow to green or blue and tells the parents to change the diaper. 

Characteristics of the ink used in the ink wetness indicator

  • No-toxic and non-VOC
  • Non-flammable and not stimulate the skin
  • Long storage time and stable performance
  • No smell and clean to use
  • Excellent fluidity and less ink is required to show the wetness
  • Excellent wear-resisting and adhesion
  • High glossiness on the surface, along with intense color.
  • Fast dry off wetness indicator. 

Is there any chemistry associated with a wetness indicator?

First of all, clear your mind that chemical component is not a limited concept. All the beauty and daily care products that we use more or less involves the chemical components. So, we should pay close attention to only those chemical components that hurt, not to all of them. In the case of a hot melt wetness indicator, it is a simple chemical reaction, while in the case of an ink wetness indicator it is just a physical reaction. So, we can conclude that indicators used are not the chemical reaction, but the color change itself is a chemical reaction. 

Can diaper wetness indicators hurt a baby?

Once the consumers see the involvement of chemical components in the baby’s diapers, they start to feel unsettled. They think that these chemical components can result in skin reactions and allergies because the skin of the babies is sensitive and less resistive. Now the question is whether the color wetness indicator can hurt the baby or not? 

The answer is a big no. As the characteristics of both indicators are mentioned above, adhesives are non-toxic and non-irritation. Diapers consist of three parts named as a top sheet, back sheet, and an absorbent core. Wetness indicators are covered in the back sheet, and it is for the convenience of mothers. This back sheet is the farthest layer from the skin of the baby. So, chemical components can’t even touch the baby’s skin, so how can they cause irritation? It is not easy for the components to pass through the strong resin wall and hurt the baby’s skin. If still, parents feel that these indicators can damage the baby’s health, so the international organizations should ban such products. 


Wetness indicators can benefit in lots of ways. It can save money and environmental footprint. When the parents know when to change the diaper, it will save lots of cost, and the only limited number of diapers will be disposed. On the other hand, all the wetness indicators are not created equal. Indicators that are of high quality will be safe to use, water-resistant, thermal, and environmentally stable, and color changes sharply. 

So, no need to worry about the dangers of wetness indicators. These are safe to use and don’t even touch the skin of your baby because indicators are present in the back sheet of the diaper. Still, if the parents are uncomfortable and feel that wetness indicators can cause damage, then the international organization should take action to ban such products. 

Efforts have been made to get the information as accurate and updated as possible. If you found any incorrect information with credible source, please send it via the contact us form
Sky Hoon
Family Man. He is a family man and married with 1 child. Spent countless nights changing diaper and surprised how outdated diapers are. Nevertheless, there is no solution yet as a parent, just want to research more about diapers.
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