Definitions of harmless:

• adjective:   unlikely to harm or disturb anyone

  Example: "Harmless old man"

• adjective:   not producing any toxic effects
• adjective:   not threatening to life or health; not malignant

  Example: "A benign tumor is usually harmless"

• adjective:   not causing or capable of causing harm

  Example: "Harmless bacteria"

• adjective:   not injurious to physical or mental health