Where do those external radicals come from ?

From inhaling polluted air and from consuming prepared foods, containing damaged proteins or too much minerals.

Most damaged protein cannot easily be decomposed by enzymes in the digestive tract. Both decomposed- and partly-decomposed proteins are absorbed into the lymph and the blood. And in the blood radicals and enzymes decompose all substances that shouldn’t be there, step by step. Decomposing these substances, very often radicals originate. And sometimes these radicals damage cells before they are completely decomposed.