Current evidence indicates that chronic loneliness is harmful to both mental and physical health. Researchers Knowles, Lucas, Baumeister and Gardner set out to test how much truth there is in the stereotype that lonely people have poor social skills.

Lonely participants in their studies performed poorly only when they knew that the task measured social skills. When the purpose of the task was concealed, they performed well. In fact, their average scores were higher than those of participants with low levels of loneliness.

The researchers concluded that lonely people do have interpersonal skills, but being aware that these skills are being evaluated triggers anxiety. The anxiety then impairs their performance, because it makes them monitor what they do and say too closely.

To counteract this effect, in another experimental condition the researchers gave lonely participants a drink described as highly caffeinated before the explicit assessment of their interpersonal skills. In reality, it contained no caffeine. As predicted, the lonely participants began to attribute their stress symptoms to the energy drink rather than to an inability to cope with the situation, and their scores on the task improved.

Knowles, M. L., Lucas, G. M., Baumeister, R. F., & Gardner, W. L. (2015). Choking under social pressure: Social monitoring among the lonely. Personality and Social Psychology Bulletin, 41(6), 805-821.