What are anti-allergy watches?

They are commercially-available watches whose exposed parts that contact skins (cases, case back, bezels, crowns, bands, etc.) have surface treatment and materials to prevent nickel or metal allergy. They are called anti-nickel and anti-metal allergy watches respectively.
They are used for preventing an allergic reaction and a recurrence, not for medical.

If you observe any allergic symptoms or skin irritation, stop wearing the watch immediately and consult a dermatologist or an allergist.

Types and definitions of anti-metal allergy watches

Anti-nickel allergy watches	Watches whose exposed parts that contact skins have surface treatment and materials to prevent nickel allergy, which has the largest number of patients among metal allergies.
Anti-metal allergy watches	Watches whose exposed parts that contact skins have surface treatment or materials to prevent any types of currently-known metal allergies.

Currently-known metal allergens

A variety of researches have been done on metal allergens. The following 13 kinds are observed as currently-known metal allergy clinical cases (as of November 21, 2013).

Metal allergens

Hg (mercury), Ni (nickel), Co (cobalt), Cr (chrome), Sn (tin), Pd (palladium), Pt (platinum), Cu (copper), Zn (zinc), Au (gold), Cd (cadmium), Mn (manganese), Sb (antimony)

Note: Metal allergy that has the largest number of patients may be called as the Big-4 allergen (Hg, Ni, Co, Cr) or the Big-6 allergen (Hg, Ni, Co, Cr, Sn, Pd).