Learn Spanish (Spain): De tanto frotar, mi hermano ha desteñido la alfombra. - From rubbing so much, my brother has faded the rug.

Because tanto is part of a prepositional phrase starting with de, and in Spanish, prepositions are always followed by an infinitive, never a conjugated verb or a gerund like the English -ing form. The structure de tanto + infinitive specifically highlights the cause of an outcome due to excessive repetition.

Can we say por frotar tanto instead of de tanto frotar?

Yes, they are grammatically interchangeable and mean almost the same thing. However, de tanto frotar puts a much stronger emphasis on the sheer excess or accumulation of the action. It feels more expressive than just stating a simple cause with por.

Is desteñido related to the verb teñir?

Yes! Teñir means to dye or color something. Adding the prefix des- reverses the action, making desteñir mean to remove color or to fade. In this sentence, it is used transitively because the brother is doing the fading, but if the rug faded on its own, you would use the reflexive desteñirse.

Why does this sentence use the present perfect ha desteñido instead of the preterite desteñió?

In Spain, the present perfect is strictly preferred when an action has a direct, visible consequence in the present or occurred very recently. Since the rug is currently faded as a result of the rubbing, ha desteñido is the most natural choice here.