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Other environmental factors such as the perchlorates and other chemistry {{refn|name=perchlorates}}, ionizing radiation{{refn|name=ionizing_radiation}}
}}., UV radiation{{refn|name=UV}} }}, and low atmospheric pressure{{refn|name=pressure|(see}} are 3.4.3not used to restrict special regions, because some Earth microbes tolerate them. PressureThe presence of<ref multiple environmental factors simultaneously is also not used to restrict special regions because of the existence of polyextremophiles that can withstand multiple simultaneous extreme conditions{{refn|name=MarsSpecialRegions2014/>)multifactor}}.
{{quote|'''Finding 3-6''': Most terrestrial bacteria tested fail to grow below 2500 Pa. However, a small subset of bacteria havenow been identified that can reproduce (on rich hydratedagar media) in a ‘‘martian’’ atmosphere (anoxic, CO2)ataverage martian pressure (700 Pa) and 0°C. This fact isnot used to distinguish Special Regions on Mars.}}}} are not used to restrict special regions, because some Earth microbes tolerate them. The presence of multiple environmental factors simultaneously is also not used to restrict special regions because of the existence of polyextremophiles that can withstand multiple simultaneous extreme conditions{{refn|name=multifactor|(see 3.7. Polyextremophiles: combined effects of environmental stressors of<ref name=MarsSpecialRegions2014/>).
{{quote|'''Finding 3-9''': The effects on microbial physiology of more than one simultaneous environmental challenge are poorly understood. Communities of organisms may be able totolerate simultaneous multiple challenges more easily than individual challenges presented separately. What little is known about multiple resistance does not affect our current limits of microbial cell division or metabolism in response to extreme single parameters.}}}}.
In principle native Martian life could have additional capabilities, and so, be able to propagate at lower temperatures or with lower water activity (one suggestion is a mixture of water and [[hydrogen peroxide]] as internal solvent in the cells<ref name=peroxide_life>{{cite journal | title = A Possible Biogenic Origin for Hydrogen Peroxide on Mars | journal = International Journal of Astrobiology | volume = 6 | issue = 2 | pages = 147 | date = 2007-05-22 | first = Joop M. | last = Houtkooper |author2=Dirk Schulze-Makuch | doi = 10.1017/S1473550407003746 | arxiv = physics/0610093 |bibcode = 2007IJAsB...6..147H }}</ref> ). However, since these capabilities are unknown, they are not used to determine special regions.
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