Dear Uwe,

this depends on several factors: the species itself, the human and the environment. The crucial component is the human factor, that is the genetic predisposition of an individual who has a higher IgE titer than non allergic people. Than, we need to look at the type of pollen: smaller ones like Parietaria, Ambrosia, Birch and grasses require less concentrations compared to other species to induce sensitization. And lastly, it is the environment - mainly air pollution - that leads to increments in sensitization rates. For Ambrosia thresholds of 10-50 g/m3 per day are reported to induce sensitization. We are expecting results re threshold levels and allergy to be published in the near future. Best wishes

Dear Uwe, I would like to say how useful to me is the info in the Pollenflug section of Deutscher Wetterdienst site! Some of my patients including my son spend the pollen season in Germany and I need such information for my everyday practice. In my opinion the answer to your question is to be found in the section Pollenflug-Gefahrenindex - Erklärungen. Pollen concentration is described as low, mild or high according to different count numbers of pollen grains per m3 depending on the kind of plant. The stronger the allergen the lower the number. So the strongest tree pollen allergen - birch has the lowest count numbers among trees and tree pollen has high count numbers than grass pollen. The reason for that is the allergenicity of the pollen, its size, air polution and so on. As a rule to sensitize a patient just a small amount of the allergen is necessary. When you increase it you can induce tolerance instead and that is one of the principles of AIT.  So I think that even low pollen concentration can induce sensitivity in predisposed  people. And you have these data in your site. There are some publish data for the critical amount of allergen necessary for sensitization but to the best of my knowledge I do not know about any other exact pollen grains count numbers.

It is established that increasing the concentration of pollen over 25 grains in 1 cm3 of air leads to the outbreak of hay fever. Pollen diameter to 25 microns penetrate deep into the respiratory tract and causes sensitization, and of a diameter exceeding 30 μm is retained in the upper respiratory tract.

The response of Alima Akhunova is very good. The development of a sensitization is related to the size of the pollen, the number of pollens inhaled, the meteorologic conditions, etc. Caution to the epidemics of asthma during and/or after the thiunderstorms where inframiconic particles or pollen are discharged.

Thanks so far for your answers. Are there any scientific papers or clinical studies supporting your statements?

Let us all just bear in mind that sensitization thresholds are subject to all the factors mentioned already and, hence, may differ between geoclimatic region (even within the same country), among patients (depending on quality of life, location of residence etc.) and so on. And last, but certainly not least, this variation may be highly variable and displaying more frequent 'extremes' because of the ongoing climate change, which is a suspected responsible for increased rated of sensitization (at least in Europe).

Regarding references, to my knowledge, there are no consistent and conclusive, multi-centre studies providing the state of the art on the field. However, some useful and fast citations could be those of:

Bousquet et al. 2004. Allergy 59.

Caillaud et al. 2014. International Archives of Allergy and Immunology.

Kontou-Fili. 2001. Allergo-Journal 10.

Sofiev M., Bergmann K.-C. 2013. Allergenic pollen. A review of the production, release, distribution and health impacts. Springer, United Kingdom.

The allergen (pollen or other) as a cause of allergic diseases acts on the body in certain conditions, which may contribute to its action, which will lead to the development of disease or hamper his actions and thereby prevent development of the disease. Therefore, despite the many allergens surround us, strikes only a small percentage of people. In itself, only the high content of grains of pollen in the air affects only the already sensitized body.

Frankly, I have no answer to this question and I guess we will never know why one person may develope IgE-antibody and the other not even if the have the same exposure in terms of quantity and period of time.

The degree of individual atopic disposition that means the genetically background for the production of IgE antibody is different and the number of factors influencing the production of the antibody is high. So - we have to wait for many years to understand the individual threshold for sensitization.

Thank you for the interesting question.

Everybody tried to give you a response (his response). But, as write K. CH. Bergmann, it is impossible to give you the response you want. The number of factors eliciting an IgE-production is high and related to each individual subject !!!

Thank you all for your contributions to the discussion!