What are the exact risks of drinking alcohol in a too high concentration?

Question

It is frequently mentioned that drinks of very high ABV should not be drunk neat because of their harmful effects. Examples of such claims can be found e.g. here: What is the strongest drink in the world?

I'm curious though, what the exact hazards are? Obviously I'm asking about hazards that stem from the concentration alone and not from the quantity, which is the easier to overdose the higher the concentration is. In other words, how is it worse for health to drink a shot of 95.6% rectified spirits than to drink the same amount of alcohol, but diluted fairly with water?

Answer 1

Here are some hard alcohol risks.

Hard Alcohol Risks:

Hard alcohol consumption is contraindicated in certain segments of the population because of the latter’s higher susceptibility to the effects of the beverage. For instance, individuals who have difficulty sleeping, or suffer from depression or other mental disorders, are advised against intake as the psychoactive mechanism of the drink can further worsen said conditions. Consumption is also strongly advised against in pregnant women as it can lead to severe gross motor development, fetal alcohol syndrome, and sudden infant death syndrome, to name a few, in children who got exposed to hard alcohol in the womb. Persons who have to deal with chronic gastrointestinal disorders like irritable bowel syndrome have to steer clear as intake can severely aggravate the conditions as well.

This beverage has a substantial concentration of ethanol per volume as well. Excess ethanol consumption inflicts sever damage to the liver and can bring about scarring or cirrhosis, inflammation or alcoholic hepatitis, and even cancer of said organ. This type of alcohol is associated with other cancers such as those afflicting the mouth and pharynx, the bowels, the breasts, the prostate, and the stomach.

Hard alcohol has a powerful diuretic effect as well. Because this is the case, individuals who have diarrhea, renal problems, or other medical conditions that are prone to severe dehydration must avoid consumption of this drink as well. Such fluid-draining effect of hard alcohol can instigate premature wrinkling of the skin due to dehydration, and may increase the frequency and severity of dermatological allergies like psoriasis and eczema. - Secrets of the Superhuman Food Pyramid: Negative Effects of Hard Alcohol

These are just the tip of the iceberg, for drinking those extremely high levels of alcohol could lead to alcohol poisoning very fast and thus cause unconsciousness or even worse, death.

Alcohol overdosing is nothing unusual. It’s hard to come across anything beyond 40 percent at bars (unless on demand) because the higher the ABV (alcohol by volume), the higher are your chances of you getting knocked out. But still, there exists a dark land of spirits where ABV can go up to a suicidal 96 percent.

Spirytus Rektyfikowany (96% Alcohol)

The purity of rectified spirit has a practical limit of 95.6% ABV; this hard to pronounce Polish Vodka is a murderous 96% ABV. In short, abusing this drink can literally make you meet God! Spirytus is actually more potent than the widely-known Everclear and sits atop as the world’s strongest alcoholic beverage. - 10 Alcoholic Drinks So Strong They Can Knock Out The Manliest Of You

Answer 2

I would take this source with a grain of salt, it doesn't link to any studies, it's from a commercial site, and there are spelling errors. The spelling errors however could be attributed to the author being a non-native english speaker, they claim to be a doctor from a seemingly well regarded medical school in China.

Safe for the stomach rate of alcohol

Any alcohol above 40% of course damages the mucous membranes (chemical burn) [...] Strong alcohol provokes esophagitis, gastritis, gastro-duodenitis.in constant use are formed of chronic inflammatory diseases and are prerequisites for cancer of the esophagus and stomach.

The above statements can be somewhat corroborated, through more reputable sources. The Oklahoma State Government has patrol officer training material that describes how alcohol passes through the body and it's effect. The training is relatively easy to follow and in my opinion, interesting. The takeaway here is that alcohol is not digested. It is absorbed mostly by membranes in the esophagus, the stomach, and the small intestine. The rate of absorption is in part determined by an equilibrium with alcohol and water on either side of the membrane. This means that the higher concentration of alcohol, the faster it's absorbed into your body. This article published in Clinics in Liver Disease, an Elsevier journal, goes over some of the fancy chemistry and largely goes over my head. However it has this to say...

Alcohol has irritant properties and high concentrations can cause superficial erosions, hemorrhages and paralysis of the stomach smooth muscle.

It also says

Peak blood alcohol levels are higher if ethanol is ingested as a single dose rather than several smaller doses, probably because alcohol concentration gradient will be higher in the former case.

So even after drinking the same amount of alcohol you may have a higher BAC, and your body processes higher concentrations of alcohol differently than lower concentrations. It can be rough on your stomach. That said, having a meal before you drink does a lot to slow the rate of absorption.

I believe that most of the concern people have about high ABV drinks, at least in the United States, stems from rumors about moonshine. Moonshine is one of the most widely known high-alcohol spirits. If improperly made it can blind or kill you. Many people don't understand what causes these effects and associate it with the high-alcohol content. However these side effects are usually caused by wood-alcohol, a byproduct of poor distilling technique. They can also be caused by lead-poisoning, which can happen if you make booze in lead pipes. "Moonshine" that you see in the store is regulated and safe.