An allergy can be explained a response of the immune system to a foreign substance. Allergies are divided into different types and these types have further sub-divisions. The major classes are respiratory allergies, skin allergies, food allergies and a class of miscellaneous allergies. The sub-divisions in these classes are as follows:

Respiratory allergies

• Summer allergies: The trigger in this type of allergies is pollen from weed and grass.
• Winter allergies:  If the trigger is something found indoors, such as allergies from mites or molds, they will affect you more in the winters as a higher amount of time is spent inside during this period.
• Spring allergies: While there is no particular cure for allergies that pop up during this season, several kinds of medication and changes in habits can help in coping with them.
• Fall allergies: In this season, the allergies are usually triggered by mold, ragweed and dust mites.
• Dog and cat allergies: About 37% to 47% of American households have a dog and as per the reports, about 10% of the American population has cats. Cat allergies, however, are known to be more common than dog allergies.
• Hay fever: This condition is also known as allergic rhinitis and attacks the individual in the form of an immune response when they come in contact with pollen grains or similar substances. This condition is further divided into two types— seasonal and perennial. While the former occurs only in the seasons when plants pollinate, the latter can affect an individual throughout the year.

Food allergies

• Milk allergy:  Also known as lactose intolerance, it is best to avoid all products which involve milk in them in order to avoid any kind of detrimental reactions such as hives, vomiting, or immediate wheezing.
• Casein allergy: Milk has a protein called casein which can act as an allergen. If consuming milk products leads to swollen lips, hives or any other symptoms it could be because of an allergy to casein. Another protein in milk that could cause an allergy is whey.
• Egg/ wheat allergy: While it is difficult to avoid egg or wheat as they are present in most of the foods, if an individual is prone to allergies from them, they should be forgone.
• Nut/fish/soy allergies: If an individual has an allergic reaction to just one type of nut or only one variety of fish, it will still be better to refrain from consuming other types of nuts/fish. One should also look out for their presence in different products such as soybeans in processed foods.
• Sulfite sensitivity: Sulfites are used as preservatives and enhancers. Check the ingredients of products if allergic to this ingredient.
• Allergy to certain herbal plants: Ginger is considered to have some of the finest healing properties. But in rare circumstances, it also causes an allergic reaction in certain people giving way to breathlessness followed by other reactions.

Skin allergies

• Contact dermatitis:  This leads to adverse immune reactions when the individual touches something.
• Allergies to poison ivy, sumac, and oak: Urushiol is the allergen that triggers a reaction in these cases.
• Allergies to insect stings.
• Cosmetic allergies
• Nickel allergies

Allergies can also be caused due to drugs like penicillin and aspirin too.