Sooty mold on a metal fence. It is feeding on sap pooped out by insects in a nearby tree.
I know that is what happened to this fence first hand, because this is a photo of my own fence.
Can Sooty Mold or Outdoor Molds Make Me Sick?
What is Sooty Mold
If you have black mold growing on your bushes, sidewalk, roof tile, patio furniture, or exterior walls you are not alone.
This condition is a very common problem. It is typically common sooty mold.
This outdoor black colored mold resembles soot, which is the black particulate residue that is deposited in fireplaces and barbecue grills after repeated exposures to fire.
It typically consists of Cladosporium mold, or other molds as well as some green algae that may occasionally be growing along with the mold.
This type of mold is found on exterior shady walls in moderately moist to wet climates. You may find it in the South East, The Mid West, New England, and The Pacific North West in the United States. It grows all around the world in cool damp and also hot humid climates.
Small Amounts of Sooty Mold and Your Health
This inspector has not seen a likely strong correlation between this mold and health complaints. This is likely because in many cases the amount of the mold is not extreme, and people likely do not sit around it for extended periods of time outside. If you have small amounts of sooty mold on your exterior walls then it becomes diluted by the outdoor air. Like some rude person urinating in a swimming pool, by the time it gets to you it is diluted and you will likely not notice it. Many people likely pressure wash it away before it gets too bad. These reasons may be why I have not found people complaining of it making them sick.
Large Amounts Of Sooty Mold
I have seen large amounts of this mold growing outdoors on lawn furniture, and on roofs and awnings a few times. Sometimes when walking under awnings at an outdoor market such as a flea market I can smell it, when I look up I see it. No one else notices it but I do because as an inspector it is what I do for a living. I have seen some bad cases on the nylon screens of screen enclosures. I remember seeing massive amounts on a porch screen during a mold inspection in the Florida Keys. The black colored mold is invisible on the black screens but I can smell it. Whenever I have taken tape samples of it from screens the mold is easy to see on the tape. The lab always has reported it to be Cladosporium mold.
Large Amounts Of Sooty Mold and Your Health
If you have large enough amounts of sooty mold on your exterior walls or patio, or roof, and if you can also smell it, and it shows as being elevated in air samples, then it would be no surprise at all if the mold could cause health reactions. However, if it is not releasing unusual levels of spores or mold odors because it is being diluted by outdoor air then it might not cause problems. These are just my ideas. I have no experience with this outdoor mold ever causing health problems. The saving grace of this mold issue is not the type of mold, but it is the fact that because it is outdoors, it is usually diluted by outdoor air.
Personally, I would not want to sit on any lawn furniture that this, or any mold is growing on because that would be direct skin contact. I have seen 1/2 dozen clients over the years with doctor verified mold related skin reactions after coming into contact with indoor moldy surfaces. These were all cases with contact with moldy clothes and furniture indoors.
Most of the stains at the base of this tree are not mold. Such growths are a part of nature and best left alone to play their part in the natural world. Click here to learn more about them.
Look A likes
Many times, people see algae or other primitive plant like growths on exterior surfaces and feel it is mold.
Algae, moss, lichens, and many other green outdoor growths are not mold and not typically considered a health threat.
But green algae growing outdoors can be a slipping hazard when wet if it is allowed to grow to excess.
In Conclusion
In conclusion I would not panic over black mold outdoors. After years of mold testing I have no personal experience of people complaining of health problems when around black sooty mold. Mold in elevated levels is a known allergen and asthma trigger. Because mold causes health complaints I would want to rectify excessive outdoor mold growth around the home before it got too bad. I would want to rectify excessive outdoor growths of green algae if it posed a slipping hazard when wet.
Seek Professional Advice
If you really feel that mold outside your house is making you sick do not hesitate to contact a doctor to get some real medical advice. Do not rely on the information on this site as medical advice. It is not to be used as medical advice, not to be treated as a definitive scientific study. I am just sharing my limited experience and personal knowledge.
Call a local Certified Indoor Environmentalist, Certified State Mold Assessor, or Certified Industrial Hygienist who holds any required mold licenses for inspections of any specific mold problems you may be having.