In many cases of skin allergies, such as those in metal allergies or other contact dermatitis, topical glucocorticoids, or specifically cortisol (hydrocortisone) is commonly recommended by doctors. These compounds have very potent anti-inflammatory and immunosuppressive properties, and thus improves the condition quite fast.

But how they work, really? Well, it's not really clear yet. But this much is known:

Glucocorticoids work by dampening the inflammatory response to the allergen, but precisely which cells they affect and in what way have not been determined for contact dermatitis.

Definitely more room for research. If the specific mode of action can be deciphered, it can imply better targeted medications, with possibly less side-effects.