While efflorescence itself isn't usually harmful to brick, it can potentially cause scarring if the mineral deposits become too heavy. That's why it's a good idea to have it washed off by a brick cleaning professional who can remove the efflorescence without damaging the brick.
Efflorescence is pretty common on brick surfaces, especially older ones. However, heavy mineral deposits or rapidly accumulating efflorescence can be an indication that your brick is undergoing harmful moisture exposure. If it becomes a concern, you may want to apply a waterproof sealant to your brick, fix its drainage outlets, and take other steps to protect your masonry from mold damage.