Eating more acidic or alkaline foods is not related to an increased or decreased risk of COVID-19 infection. Widely circulated social media posts falsely suggest that the pH of COVID-19 ranges from 5.5 to 8.5. Often these posts advise readers to eat alkaline foods (specifically fruits and vegetables) with a pH of more than 8.5 to prevent COVID-19.  Viruses themselves do not have pH levels, because they are not water-based solutions.In chemistry, pH (power of hydrogen, or potential for hydrogen) is a scale used for water-based solutions to indicate if they are acidic (pH below 7, with a lower pH indicating a stronger acid), neutral (pH around 7), or basic (pH above 7, with a higher indicating a stronger base).

Since viruses are not water-based, the pH scale does not apply to the novel coronavirus SARS-CoV-2, the disease that causes COVID-19.While some illnesses or medications may cause blood pH levels to increase or decrease in our bodies, foods eaten as part of a regular diet do not have a significant impact on blood pH. Saliva and urine pH may change in response to diet, but these changes are variable from person to person and will not prevent or cure COVID-19.

Many claims about alkaline foods preventing COVID-19 refer to a 1991 paper in which another type of coronavirus, the coronavirus mouse hepatitis type 4 (MHV4), was studied in mouse or rat cells in a solution with a pH of 5.5 to 8.5. Mice and rats are not the same as humans, and this study was not conducted in humans or on human cells. In addition, MHV4 is not the same as the SARS-Cov-2 virus that causes COVID-19, and this study was performed well before the SARS-Cov-2 was discovered in 2019.

Eating a well-balanced diet including a variety of fruits and vegetables can help support immune function which may help to prevent illness in general, but there is not enough evidence to suggest that a well-balanced diet would be effective in preventing or treating COVID-19. 

In chemistry, alkaline is an adjective that is sometimes used to describe a subset of bases that dissolve in water. Alkalinity, however, is a different term used by oceanographers and hydrologists to describe the capacity of water to resist pH changes that would make it more acidic, in contrast to basicity which refers to a measurement on the pH scale above 7. When food is described as alkaline, this is often based on misconceptions about the impacts of eating food on the pH of the body. Fluids associated with various organs and tissues in the body have different typical pH levels; for example, the stomach operates at an acidic pH for digestion. Eating food does not have a significant impact on blood pH as this is regulated by the body to stay relatively neutral (pH of 7.35 to 7.45).

One social media post incorrectly applies a research study about another type of coronavirus called mouse hepatitis type 4 (MHV4), and also lists food items with pH values that are inaccurate. For example, lemons are falsely listed to have a pH of 9.9 (the true pH is closer to 2-2.6) and avocados with a pH of 15.6 (the true pH is likely 6.27-6.58). For reference, the pH scale only goes from 0 to 14, and food products are generally within a pH range of about 2 to 8. The claims made by this post, with several versions circulating on multiple social media platforms (including Facebook, Twitter, Telegram, and WhatsApp), have been widely debunked by health experts, fact-checkers, and journalists.

Another social media post urges people to consume a hot drink made with lemon and baking soda (sodium bicarbonate), making the false claim that the mixture "immediately kills the virus [that causes COVID-19], removing it completely from the body" when there is no evidence for this in published scientific or clinical research. The post also incorrectly claims that lemon and baking soda "alkalize the immune system...at nightfall," when "the system becomes acidic and the defenses are weaker."

While baking soda is alkaline, lemon is actually acidic. Furthermore, consuming foods of different pH is unlikely to significantly impact the pH of most parts of the body (ex. blood pH). While the acidity of various parts of the body can change throughout the day and night (ex. gastric acid secretion, pH of the mouth), this is usually not a cause for concern unless there are medical issues (ex. dental diseases). Additionally, the immune system is active and plays an important regulatory role in the body during sleep - in fact, research has found that the lack of sleep can interfere with immune system function. Research does not back the claims made by this post circulating on social media platforms like WhatsApp.

It is important to note that consuming more alkaline food or drinks will not change the risk of COVID-19 infection or treat COVID-19.