The main ingredients in most oven and drain cleaners are sodium hydroxide (lye), a caustic that can cause burns to the skin and, in severe cases, blindness, and sulphuric acid, a corrosive chemical that can also cause severe skin burns and blindness. Both work by eating away at whatever is in their path. Most oven cleaners come in aerosol containers so that, in addition to lye and sulphuric acid, you are also exposed to propellants. The reason why oven cleaners are made with lye is simple. When lye mixes with the grease in your oven, it makes a crude soap, which is then used to facilitate cleaning.
Strong alkalis can be used on cold ovens. However, there are newer types of oven cleaners which use less alkali. These need to be used on warm ovens to aid removal of grease and grime. The vapours from both types of cleaners are still highly toxic.
Prevent messy grime from building up by placing a sheet of aluminium foil on the oven floor. This will catch most spills and can be changed as often as necessary
Use baking soda. This can be sprinkled into the oven while still warm to loosen grease and then wiped away with warm water. Or you can make a spray from 3 tablespoons of baking soda dissolved in a pint of warm water. Spray on and wait 20 minutes. Scrub off with a fine scouring pad if necessary. Baking soda is effective for lightly to moderately soiled ovens. Heavily soiled ovens may require a different approach
Use vinegar. Using the same principles for unclogging a drain, you can spray a solution of white vinegar into your warm oven. Sprinkle with baking soda, leave for a few minutes to bubble and then scrub.