Among the biological particles present in the air, pollens are among the main factors of respiratory allergies. THE National Aerobiological Surveillance Network responsible for studying the content of biological particles in the air and measuring their consequences on health, brings us its expertise on this subject.

Where do pollens come from?

The pollen grain is the microscopic reproductive element produced by the male organs of plants (anther stamens). When it disperses, the pollen grain contains two or three cells. The outer layer of the pollen grain is composed of a very resistant substance called "sporopollenin" which allows it to be distributed in the environment without being damaged. The shape of the pollen grains and their ornaments are characteristic of the plant that produced them and thus allow them to be identified.

How are pollens transported?

Once produced by the anthers, the pollen grain must then reach the style, that is to say the female organ of the plant, so that fertilization can take place, thus forming a seed which can germinate and give birth to a new plant.

Unlike animal species, the vast majority of plants carry both female and male organs on the same flower: they are said to be "hermaphroditic" or "bisexual".
On the contrary, some plants have separate sexes and have both female plants which carry the style and male plants which carry the anthers. They are “unisexual” plants and both male and female plants are required for fertilization to take place.
Pollen produced by male organs must therefore be transported to female organs.

This transport can be carried out in several ways: 

• Thanks to insects in so-called “entomophilous” plants

Flowers that use insects to reproduce are usually showy, fragrant, nectar-rich, and hermaphroditic (roses, dandelions, daisies, fruit trees). Their pollen is not abundant in the atmosphere and not very allergenic.

• With the wind in so-called “anemophilous” plants

At different times of the year, pollens from trees and plants fill the atmosphere. Transported by air, they sometimes travel great distances (all the greater because their size is small and their weight is lighter). Flowers that use wind are generally inconspicuous, dull, odorless or nectar-free, and unisexual (grasses, sorrel, mugwort, ragweed, cypress, birch). Their pollen is abundant in the atmosphere and often allergenic.

What are the most allergenic pollens?

The most allergenic pollens are those carried by the wind (anemophilous plants). Their size is 20 to 60 micrometers on average.

Among the trees, the most allergenic are:

• Betulaceae in the north of France with birch, alder and hazel.
• Conifers, with an important role of cupressaceae which have become very present through the planting of hedges or ornamental trees. Pine plays a minor role.
• The plane trees.
• Oleaceae including olive, ash and privet.
• The Oaks.

Among the grasses:

• Phlelola.
• The tares.
• The dactyl
• The bluegrass.

Among the herbaceous:

• Plantains.
• Mugwort in the north and ragweed in the south-east of France, and particularly in the Lyon region.
• Chenopods.
• Urticaceae with the parietaria on the Mediterranean rim.