One of the more common asthma triggers is mold. And like tree and grass pollen, mold is something that is next to impossible to completely avoid.  Mold grows pretty much anywhere there's moisture, which basically means mold is ubiquitous -- it's everywhere.

Mold is known to be both trigger of asthma symptoms, but new evidence suggests it also may cause asthma, which I wrote about here.

According to the Environmental Protection Agency (epa.gov) mold is microscopic fungi that live on plant and animal matter.

And it's not necessarily the mold itself that triggers asthma but tiny microscopic spores the mold produces to reproduce.  These get into the air and are easily inhaled.  For most people they are innocuous, meaning they don't cause any harm.

But for those of us with allergies to mold our immune systems develop an "abnormal" reaction to the mold spores.  In this way, the first time you're exposed your body generates mold spore IgE, which is basically an antibody that is specifically trained to recognize mold spores.  Your body is now sensitized to mold spores.

Every subsequent time you're exposed to mold sports your immune system treats them as an enemy combatant.  The spores are recognized by mold spore IgE.  The IgE takes the spores to a mast cell and this triggers the mast cell to release mediators of inflammation, such as histamine and leukotrienes.

These mediators cause tissues lining your eyes and respiratory tract to become inflamed, and this is what causes your common allergy and asthma symptoms:  itchy, red and watery eyes, stuffy nose, sneezing, wheezing, etc.  

According to the Asthma and Allergy Foundation of America (aafa.org) outdoor mold allergies are most prevalent at the end of July to late summer.  They are generally spread by the wind.  Peak mold times are pretty much dependent on the type of mold.

There are many molds, but the following (in case your scientific minded) are the specific ones that are known allergy/ asthma triggers:

• Alternaria
• Cladosporium (Hormodendrum)
• Aspergillus
• Penicillium (hence your allergy to antibiotics)
• Helminthosporium
• Epicoccum
• Fusarium
• Mucor
• Rhizopus
• Aureobasidium (pullularia) 

There's really not much you can do about outdoor molds.  However, some can be avoided.  For example, it comes highly recommended that work in these areas be left for someone else to do. Or, at the very least, you can wear a protective mask so you don't inhale the spores.

The aafa.org also notes that mold, unlike pollen, doesn't die off during the winter months.  In fact, mold pretty much stays dormant during the winter months, and then "grows on vegetation killed by the cold."