What is the difference between Undoing and Reaction Formation?

According to wikipedia:

Reaction formation is a defense mechanism in which emotions and impulses which are anxiety-producing or perceived to be unacceptable are mastered by exaggeration of the directly opposing tendency

Undoing is a defense mechanism in which a person tries to cancel out or remove an unhealthy, destructive or otherwise threatening thought or action by engaging in contrary behavior

Both defense mechanisms seem to be reacting to an unhealthy thought with the opposite. Is there a quality that differentiates the two mechanisms?

Wikipedia links:

• https://en.wikipedia.org/wiki/Reaction_formation
• https://en.wikipedia.org/wiki/Undoing_(psychology)