Acidification refers to the process of increasing the acidity of a substance. During the acidification process, the pH level of the substance decreases. The pH value gives a measure of a substance's acidity or alkalinity. The lower this value is, the more acidic the substance. Human eyes (just like the skin) have a certain pH value. If this pH value is disrupted, health complications may occur. Acidification of some parts of the eye (like cornea) may be caused by hypoxia (lack of oxygen).

The cornea of the eye must receive enough oxygen for health and comfort. If contact lenses cause a lack of oxygen to reach the cornea, this can trigger acidification and potential health issues. Contact Lenses have different levels of oxygen permeability. This „transmissibility“ is measured in Dk/t. The permeability of oxygen is one of the most important factors for contacts.