The mum, a psychologist who specialises in addiction, doesn't see the point in trying to stop the habit she has had since when she was little. Thumb sucking can be a hard habit to kick, as Marlene Headington, a psychologist specialising in addiction, knows. She has been sucking hers for 37 years. “It feels comforting,” she says. She reserves her habit for bed, although her thumb still sneaks into her mouth when she is tired or stressed.