Can anyone explain the humidity levels to me causing mold?

Humidity is moisture in the air. The area is staying too damp making it a perfect area for mold to grow. If you can I would purchase a dehumidifier for the area. You can get rid of the mold by spraying it with a mixture of bleach and water. You might even want to consider painting the wall with a paint made for walls in areas with high moisture.

Is the wall near an air conditioner unit or vent? You could also have some sort of leak in the wall. Maybe roof leaks and it's running into the wall.

Mold-Advisor.com

from: energystar.gov

Reducing indoor humidity

• Do you have a crawlspace under your house? A dirt floor in a crawlspace should be covered with plastic (vapor barrier) to prevent moisture from the soil increasing humidity levels in your home. If there is standing water or the soil is wet, dry it out with fans before covering the floor.
• Use ventilation fans in kitchens and baths to control moisture. Check to make sure ventilation fans venting directly outside. In some cases the vent fan may have been installed to vent into the attic or become disconnected or blocked.
• Your clothes dryer should be vented directly to the outside. Inspect the vent duct. Make sure it is attached securely to the dryer. Check that it is clear of obstructions (e.g. lint). Check for holes that leak air. If vent duct is damaged replace it with a metal duct. The vent duct should be cleaned at least once a year. The Consumer Products Safety Commission additional safety tips for dryer vents .
• Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly.
• Ask a heating and cooling contractor to check your heating and cooling system to make sure it is sized and operating properly to remove humidity. If you system is too big or the airflow incorrect your air conditioner will not remove humidity like it should. Also, ask the contractor to check your duct system for air leaks, and proper size and air flow to each room.

Sealing air leaks (Home Sealing) and sealing duct air leaks can help to prevent high humidity levels in your home.

http://moldpedia.com/what-causes-mold-grow

100% percent humidity is raining, 74 percent is high, but not unbearable. I would get a dehumidifier and put it near the lounge wall to decrease the humidity. Keep an eye on it as it will fill up with water(distilled water). We have five large aquariums in our house so our humidity is up even in the winter. So far we have not had any mold problems. I would look into seeing if there is a water problem behind the wall also.

I don't remember, but I know that WAY too high. You should ask a local contractor

I would get a dehumidifier.

You definitely need to reduce your humidity level. 40-45% is optimum for health. My daughter has a lot of allergies, including mold, and this is the level her allergist said it needs to be at. We have a horrible with humidity in our partially unfinished basement in our 111 year old house. It was running about 80% and we had mushrooms growing on the walls. We put the money into a good dehumidifier and withing 48 hours the humidity level dropped to 60, the growths were gone and the air felt much cleaner in the house.

The dehumidifier is a great thing, I have been using this device for a long time to prevent mold. Also I'm thinking about whirlybird installation for air circulation. After reading an article about this I found out that there is an alternative to whirlybirds and it's called the Solar Whiz. I have been using solar panels as a source of electricity for a long time, so I have no questions about the efficiency of the Solar Whiz. Besides, it can ventilate a much larger air quantity and operates completely without electricity. I think, that it's ideal for roof ventilation, what do you think?

In addition to the dehumidifer, during the warmer months put a small fan in the window - air movement is your friend.

If the wall that is damp is a masonry wall, you can also paint the wall with Drylok that will keep the moisture from wicking inside. If there is no insulation in the wall molding, I have wiped down the wall with vinegar water which will retard mold growth.

There is also a spray to kill mold called Concrobium that I use in clients homes, and its almost completely odorless too.