A/HRC/20/24 Human Rights Committee has stated in communication No. 560/1993 that “every decision to keep a person in detention should be open to review periodically so that the grounds justifying the detention can be assessed. In any event, detention should not continue beyond the period for which the State can provide appropriate justification. For example, the fact of illegal entry may indicate a need for investigation and there may be other factors particular to the individuals, such as the likelihood of absconding and lack of cooperation, which may justify detention for a period. Without such factors, detention may be considered arbitrary, even if entry was illegal.” 22. The Special Rapporteur would like to stress that under no circumstances should administrative detention of migrants be indefinite. The Working Group on Arbitrary Detention stated in its deliberation No. 5 that a maximum period of detention should be set by law, and the custody may in no case be unlimited or of excessive length. The Working Group considers as arbitrary deprivation of liberty “when asylum seekers, immigrants or refugees are subjected to prolonged administrative custody without possibility of administrative or judicial review or remedy” (A/HRC/16/47, annex, para. 8 (d)). The Working Group has also stated that upon expiry of the maximum period of detention established by law, the detainee must be automatically released (A/HRC/13/30, para. 61). 23. Migrants who are detained may not always be aware of their right to request review of their detention, sometimes due to language barriers or lack of access to a lawyer. The Special Rapporteur is therefore of the opinion that periodic review of detention should be automatic. The Working Group on Arbitrary Detention has stated that there should be automatic, regular and judicial, not only administrative, review of detention in each individual case, and that review should extend to the lawfulness of detention and not merely to its reasonableness or other lower standards of review (ibid.). 24. It may sometimes be impossible to remove an irregular immigrant because, inter alia, the migrant lacks documents to be able to return to the country of origin, there may be financial or other practical impediments to removal (for instance no means of transportation available) or where there is a risk of torture in the country of return (thus the nonrefoulement principle in article 3 of the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment) prevents the expulsion or return of the person to that country. Furthermore, asylum-seekers whose life or freedom would be threatened on account of his/her race, religion, nationality, membership of a particular social group or political opinion are protected through the non-refoulement principle in article 33 of the Convention relating to the Status of Refugees. When it is impossible to remove a migrant due to reasons which are beyond his or her control, the migrant should not be detained. This has also been stated by the Working Group on Arbitrary Detention, which noted that in cases where “the legal or practical obstacles for the removal of the detained migrants do not lie within their sphere of responsibility, the detainees should be released to avoid potentially indefinite detention from occurring, which would be arbitrary. The principle of proportionality requires that detention has a legitimate aim, which would not exist if there were no longer a real and tangible prospect of removal” (ibid., para. 91). 6. Conditions of detention of migrants 25. Information gathered by the Special Rapporteur indicates that migrants are sometimes detained in unacceptable substandard conditions in overcrowded facilities with poor hygiene, limited or no sanitation and infrequent meals. The Special Rapporteur has also been made aware that mental and physical health of migrant detainees is often neglected. Doctors and nurses are not always available and may not have the authority to properly treat their patients, inter alia when they need hospitalization. Furthermore, reproductive health care for women, especially pregnant women, is not available in all places of detention. 7