Which of the following conditions can be caused by a nervous habit?

Onychophagy, commonly known as nail-biting, is a condition that is often associated with nervous habits or anxiety. Individuals who bite their nails tend to do so as a way to cope with stress, boredom, or nervousness. This behavior not only affects the appearance of the nails but can also lead to physical damage to the surrounding skin and nails, resulting in infections or other complications.

Other conditions listed, while they may have various causes, are not primarily classified as resulting from nervous habits. For instance, psoriasis is a chronic skin condition related to immune system dysfunction. Alopecia, which refers to hair loss, can result from a variety of factors including genetics, medical conditions, or stress, but it is not specifically linked to nervous habits in the same way as onychophagy. Conjunctivitis, an inflammation of the eye, has causes typically related to infections or allergies rather than behavioral factors like nervous habits.

Understanding onychophagy as a nervous habit highlights the connection between emotional states and physical manifestations, which is a key concept in both cosmetology and general health awareness.