It is know that pollen from certain trees can cause allergies. These allergies could be in various forms including itchy rashes. If you are prone to allergies there are a number of trees you should avoid including spruce, honey locust, oak, sweet gum, pine and birch. It is has observed that it is not so much related to the species of the trees as much as it is related to the sex of the tree. Trees that are single sex are found to be the ones that cause allergies. The allergen responsible for triggering this is found to be the 'male' part of the tree. Trees, however, differ widely in their pollen producing ability and their ability to trigger allergies and asthma.
Trees that produce separate male and female flowers on the same plant are called 'monecious'. Examples of these would be honey locust, spruce, birch, oak etc. With these trees there's not much you can do, as you cannot choose to grow only the female of the species.
On the other hand, trees that produce male and female flowers but on separate plants are called 'dioecious'. Examples of this species include Cottonwood, juniper, mulberry, Ash, box elder and cedar. In the case of these trees only if you select the male of the species will you have a problem.
From the perspective of allergies, the worst of the lot are dioecious males. These produce only pollen. These trees have no fruit or no seed. This is probably what is causing the allergy and the itching rash. As opposed to which the best kinds of trees to have around if you are allergic are dioecious females. These trees are allergen free as they produce no pollen.
If you are experiencing allergies caused by one or two of the species mentioned then you might want to steer clear of the following trees too. They are the male ash, sycamore, elm, alder, birch, male maple and hickory, and oak pine.
Here are a few things you can do to make sure you don't experience the irritation caused by these allergies. For starters you can plan your landscape in such a way that you don't plant too many of the trees that cause these allergies. When planning your outdoor activities make sure you plan your trips when you know that the pollen count (the number of pollen grains in the air per cubic meter) is at its lowest. A simple way to do this is just follow your local pollen index.
answered by G R