Like with our pacifiers we recommend a replacement of bottle nipples every 4-6 weeks for both safety and hygienic reasons. Keep an eye out for any changes in the surface, changes in size and shape, or rupture in the material, and replace the bottle nipple if you notice any differences. Natural rubber latex is a natural material and is affected by sunlight, high temperatures, and moisture which accelerates the aging process of the latex material. Therefore, the material changes its properties and can become brittle or sticky. Whenever you experience a change in the material the pacifier must be replaced.