The problem due to $\mathrm{Rh}^{-}$factor arises when the blood of two $\left(\mathrm{Rh}^{+}\right.$and $\left.\mathrm{Rh}^{-}\right)$mixup

Landsteiner and Weiner (1940) disovered Rh antigens in the rhesus monkey. Now, it is found in most human beings. Human with this factor are said to be $\mathrm{Rh}^{+}$and humans without this factor are said to be $\mathrm{Rh}^{-}$. The problem due to Rh incompatibility arises when the blood of $\mathrm{Rh}^{+}$person and $\mathrm{Rh}^{-}$women mixes up during pregnancy or through blood transfusion.