Is it harmful to cook with previously used cooking oil over and over again? How many times can cooking oil be re-used?

Cooking oil can be used several times before being replaced with a new one. It is important to know that any kind of cooking oil will degrade when heated. Coconut cooking oil has a higher oxidative stability and more resistant to rancidity compared to other cooking oil, but it will eventually need replacing as well. Generally, the quality of cooking oil can be seen from its colour and odour changes. When the colour of cooking oil darkens and starts to create undesirable odour then it needs replacing. The number of re-usages cooking oil greatly depends also on the type of food being cooked or fried.