Generally, a well balanced diet rich in fruits, vegetables and nuts proves to be beneficial for fighting most conditions including allergies.
Here are a few foods that have anti-allergy properties:

1. Foods rich in Quercetin: a bioflavonoid which has anti-inflammatory, anti-oxidant and anti-histamine properties. It works by stabilizing the cell membranes of mast cells and basophils, thereby preventing the release of histamine. Good sources of quercetin include onions, apples, berries, cabbage, cauliflower, and green and black teas. Research has proved that consuming diets rich in quercetin lowers the risk of certain cancers, blood pressure and hence the risk of heart disease and improves lung functioning.
2. Walnuts and Flaxseeds: These are good sources of plant based omega 3 fatty acids. A high intake of omega 3 fatty acids is associated with decreased risk of allergies especially the ones due to bad dietary habits. If you are not allergic to fish- salmon, trout, tuna, mackerel, sardines and anchovies are rich sources of omega 3 fatty acids too. Be careful while eating fish as they may have high levels of mercury. Ground flaxseeds, flaxseed oil and anchovies also have a high selenium content which is a mineral with anti-allergy properties
3. Magnesium-rich foods like cashews, almonds and kelp have excellent allergy relief effects as magnesium is an antihistamine and bronchodilator. It relaxes the muscles of the bronchial tubes and of the whole body. A study conducted on animals exposed to allergens found higher levels of histamine in those with magnesium deficiency than those with adequate magnesium levels in their bloodstream.
4. Turmeric: This native Indian spice used mainly in Ayurveda and Chinese medicine has many medicinal properties. This bright yellow colored spice contains curcumin, a powerful anti-oxidant and anti-inflammatory substance. Fresh or dried turmeric can be used to flavor foods like meat, fish, curries, rice, pastas, salad dressings, stews and vegetables or you can take supplements depending upon your lifestyle.
5. Fresh fruits and vegetables: Green vegetables and citrus fruits like lemons and oranges contain hesperitin/hesperidin. Both are potent phytonutrients, (hesperidin is bound to a sugar molecule) having antioxidative, anti-inflammatory, cholesterol lowering, anti-carcinogenic and anti-histamine effects. A research study that studied the diet of children over a year concluded that children who ate raw vegetables and citrus fruits were less likely to suffer from wheezing, shortness of breath and hay fever than children who ate white bread, margarine and processed foods.
6. Garlic: Garlic is known to have many curative properties since ancient times and this super food has been used to cure a wide range of ailments. Garlic, apart from improving heart health by lowering cholesterol, reducing blood pressure and preventing and treating cancer, can also help reduce allergic reactions. The ability of garlic to hinder the effect of certain enzymes that produce inflammatory compounds namely thromboxane and prostaglandins can help prevent allergy. Apart from this, garlic also contains a fair amount of vitamin C and selenium, both of which have anti-allergy effects.
7. Spices like horseradish, fennel, anise and hot mustard have a sinus clearing effect and act as natural decongestants, by stimulating the mucosal cilia to break up congestion, hence relieving allergies. You can add them to spicy foods and look up recipes that include them when you start feeling stuffy.
8. Vitamin C rich fruits like oranges, apples, watermelon, strawberries etc. can help relieve symptoms like hives and itchiness as it prevents histamine release, helps breakdown histamine faster once released, reduces swelling as it has anti-oxidant effecta that counteracts the effects of free radicals. Supplements or Vitamin C tablets can be taken to alleviate allergy symptoms.
9. Green Tea: Normally used to aid in weight loss, catechins (the chemical compound found in green tea) is also known to inhibit the enzyme responsible for converting histidine to histamine. Use loose green tea leaves instead of tea bags and let it stand for five minutes. To enhance the absorption and availability of catechins in the body, complement it with a substance rich vitamin C like lemon, fruit juice etc.
10. Purplish-red colored foods like beets, cherries, berries, red and dark purple grapes are rich in anthocyanin, a natural anti-inflammatory agent, thus reducing allergies. Increased intakes of anthocyanins from fruit and vegetables also reduce blood vessel hardening and improve overall heart health.