Allergies are the result of a person's body having hypersensitivity which could be to something that is drunk, ate, or applied to the body, even something in the air around us. The substance or condition that causes the allergy is called the allergen and there is no limit to what can be an allergen as everyone reacts differently to the world around us. BTW, i found a site about skin rugs in spanish : alfombras piel.
The vast majority of allergens that cause allergies in people are those found in the foods we eat in particular, peanuts and other members of the nut family. This allergic reaction to food extends even further with everyday products such as soy, rice and milk also causing problems but these are just the better known substances.
While it isn't a huge number, a few individuals even have an allergy to chocolate and other cocoa based foods but food allergies can cause problems with the respiratory, digestive and immune system very soon after consumption. Of course seafood also causes problems with some people in particular crustaceans so they should be avoided but it is surprising how many people that know they have a an allergy to something continue to take the risk as they enjoy the food so much.
Food allergies often cause reactions which are seen initially as redness, itchy areas of skin and other irritations often quite common to the family of citrus fruits. It is peanut allergies which generally cause the most concern as the reaction to them, even a simple case of contact can be extremely serious and in some cases cause death.
Although flowers are beautiful, even these can prove harmful to those individuals susceptible to their pollen, causing respiratory problems and even damage to the airways. Getting rid of plants with flowers around that individual might also help to a great extent but of course this is only if the flowers have been detected as the actual cause of the allergy.
Although a reaction to nickel is not unusual to most people, a very small number of individuals even have an allergic skin reaction to silver and gold. Individuals reacting to metals are liable to break into hives or the skin starts itching along with swelling in that area, turning red or purple in the area coming in contact with the metal is another common reaction.
If you know you may have an allergy, avoiding, the substances is the first course of action but allergies can change or become more pronounced so regular allergy testing should be carried out as a form of preventative measure.