Solitude
Solitude is a state of seclusion or isolation, i.e. lack of contact with people.  It may stem from deliberate choice, contagious disease, disfiguring features, repulsive personal habits, or circumstances of employment or situation (see castaway).
Short-term solitude is often valued as a time when one may work, think or rest without being disturbed. It may be desired for the sake of privacy.
A distinction can be made between physical and mental seclusion. People may seek physical seclusion to remove distractions and make it easier to concentrate, reflect, or meditate. However, this is not necessarily an end in and of itself. Once a certain capacity to resist distractions is achieved, people become less sensitive to distractions and more capable of maintaining mindfulness and staying inwardly absorbed and concentrated. Such people, unless on a mission of helping others, don't seek any interaction with the external physical world. Their mindfulness is their world, at least ostensibly.

# Health effects
Symptoms from externally imposed isolation often include anxiety, sensory illusions, or even distortions of time and perception. However, this is the case when there is no stimulation of the sensory systems at all, and not only lack of contact with people. Thus, by having other things to keep one's mind busy, this is avoided.
Still, long-term solitude is often seen as undesirable, causing loneliness or reclusion resulting from inability to establish relationships. Furthermore, it might even lead to clinical depression. However, for some people, solitude is not totally depressing. Still others (e.g. monks) regard long-term solitude as a means of spiritual enlightenment. Indeed, marooned people have been left in solitude for years without any report of psychological symptoms afterwards.
In contrast, some psychological conditions (such as schizophrenia) are strongly linked to a tendency to seek solitude.

# Different types
There are two different common types of human isolation. These are known as protective isolation and source isolation. They are different in that one is voluntary, while the other is not.
Protective isolation is the type of isolation created in tests. This can usually be classified by the fact that one can opt out of the experiment, or the isolation. It can often be prepared for, and is generally not a negative thing. (More often than not, there is a reward for the subject's time as an experiment.)
Source isolation includes no benefits, and cannot be prepared for. Thus, it is usually undesirable, and is not very common.
Emotional isolation is a term used to describe a state of isolation where the individual is emotionally isolated, but may have a well functioning social network.

# Other uses

## As a punishment
Isolation, in the form of solitary confinement is a punishment used in many countries throughout the world for prisoners accused of serious crimes, those who may be at risk in the prison population (such as pedophiles), those who may commit suicide and those unable to participate in the prison population due to sickness or injury.

## As a treatment
In addition, psychiatric institutions may also institute full isolation or partial isolation for certain patients, particularly the violent or subversive, in order to minister to their particular needs and protect the rest of the recovering population from their influence.