The reason for sperm damage from most products can be seen when data on product pH and osmolarity are compared as in the following table.
The optimum pH value for sperm migration and survival in the cervical mucus is between 7.0 and 8.5 (according to the World Health Organization manual for examination of human semen and sperm-cervical mucus interaction 4th edition 2000). Sperm are very sensitive to low (acidic) pH and, to a lesser extent, elevated (alkaline) pH. Below pH levels of 6.9, sperm die at a rate that increases with lowering pH.
Sperm are also sensitive to both high and low osmolarities (ion concentration in solution) because these can cause them to either shrink or swell beyond their “critical volume limits”. A physiologic osmolarity* around 360 mOsm/kg (that of semen) is best for sperm function.