There is no safe amount of alcohol to drink before people put themselves at risk of blacking out, a review of studies concludes. Individual biological differences, not just alcohol consumption, influence the risk of blackouts, Medical Daily reports.

Scientists from the Research Society on Alcoholism reviewed 26 studies on alcohol-induced blackouts published in the past five years.

Alcohol-induced blackouts, or memory loss for all or portions of events that occurred during a drinking episode, are reported by approximately 50 percent of drinkers, the researchers wrote in Alcoholism: Clinical & Experimental Research. Blackouts are associated with a wide range of negative consequences, including injury and death.

A study published in 2014 found that among teens who drink, 90 percent have blacked out after drinking at least once by the time they reached age 19. Teens who black out after drinking are more likely to be female.

When a person blacks out, they appear to be awake, alert and intoxicated, but they have no memory of what has happened. At high enough doses, alcohol impairs the acquisition of memory.

Females are more likely to black out because they weigh less and have less body water to dilute the alcohol, the researchers noted. The study included 1,402 teens ages 15 to 19 who drank. Other risk factors for blacking out after drinking included smoking, having sensation-seeking and impulsive behaviors, lacking conscientiousness and having friends who also drank or used other substances.