Drinking lemon water makes your skin darker

It is commonly said that a white complexion can cover up a hundred uglinesses. Whitening is an eternal topic for people who love beauty. White skin makes people look more energetic. As long as the skin is white enough, no matter whether your facial features are delicate or not, or whether you have long legs, you will still look very good. Currently, many female friends are pursuing ways to become beautiful. Some say that drinking lemon water can whiten the skin, while others say that drinking lemon water can make the skin darker. What is the reason for this? Next I will introduce it to you in detail.

I never thought there were so many problems with lemons. Of course, the most noteworthy thing is the rumor that lemon water cannot be drunk during the day and will make you turn black, which makes it seem like drinking lemon water is something that must be done secretly in the dark and cannot be seen in public.

Lemon water cannot be drunk during the day

1) Lemons contain photosensitive substances (limonene, coumarins, mainly coumarins), so they are sensitive to light, so drinking them during the day will make people darker;

2) Lemon contains vitamin C, which dies when exposed to light. Of course, we can also say the other way around, it is indeed impossible to verify why the specific statement was circulated in the first place.

2. Lemonade: Scientific Analysis of Photosensitivity

Lemons, including other citrus fruits, contain coumarins, also known as psoraleae. This type of substance is photosensitizing and accounts for about one-third of the oil extracted from citrus peels. If they are not removed from essential oils and are applied to the skin and exposed to sunlight for a certain period of time, photosensitivity reactions will occur.

The so-called photosensitivity reaction refers to the situation where photosensitive substances enter the skin, combine with specific molecules (receptors), absorb ultraviolet rays, and cause changes in their chemical structure, resulting in irritation and toxicity, leading to an inflammatory reaction similar to allergies (solar dermatitis), skin redness, swelling, rash, exudation, etc. Melanin deposition may also occur after inflammation. But it generally does not lead to non-inflammatory melanosis of the skin. Drugs, vegetables, and flowers containing photosensitizing substances may cause photosensitivity reactions. Common plants include Apiaceae (Angelica dahurica, celery, parsnip, etc.), Rutaceae (Citrus), Cruciferae (Radish and Rapeseed), Asteraceae (various Artemisia species belong to this category), Leguminosae, Moraceae, and some fungi.

However, eating these things does not necessarily lead to a photosensitivity reaction. There are three conditions for a photosensitivity reaction to occur: 1) constitution specificity; 2) sufficient amounts of sunlight exposure; 3) sufficient amounts of photosensitizing substances. If these conditions are not met, photosensitivity reactions will not occur.

Lemon does contain coumarins and is photosensitizing, but it is too much to say that you cannot even drink lemon water during the day. Why?

Lemon does contain coumarins

1. Dosage issues

As the old saying goes: It is foolish to talk about toxicity without talking about dosage. I specifically surveyed those who are used to drinking lemon water on Weibo to ask how many lemons they consume every day. Some answered a few slices, some answered one, and some answered half a lemon. Take a middle value: half a lemon per day. A lemon weighs about 50 grams, and half a lemon weighs 25 grams. If we can extract all the coumarin from it after brewing it with water, the amount is: Coumarin amount = lemon weight coumarin content (the total coumarin content of a Brazilian lemon is 113g/100g) = 25g 113g/100g = 28.25g. If we eat 25 grams of dried lemon, we may ingest 282.5g of total coumarin. Is this amount enough to cause a photosensitivity reaction in the presence of sufficient sunlight?

Let's take a look at an experiment

J. Schlatter and others from Switzerland conducted an experiment many years ago. The sample size was small, only 4 people, but it can still explain some of the problems: the subjects ate 300 grams of celery root and then exposed it to UVA to see if it could induce a phototoxic reaction. The total coumarin content of celery root is 28.2 mg/kg, and eating 300 grams is equivalent to ingesting 8.5 mg of coumarin. The UVA photo dose reaches 9J/cm2. Most people will get tanned if they are exposed to this dose in the sun.

Examination found that the coumarin content in the blood was too low to be detected, and the subjects did not experience any phototoxic reaction. After increasing the irradiation dose and conducting further experiments with different concentrations, it was found that the dose of coumarin that can induce phototoxic reactions should be 10 mg 5-methoxypsoralen + 10 mg 8-methoxypsoralen, or 15 mg 8-methoxypsoralen. 30 minutes after ingestion, the concentrations of the corresponding components in the blood should reach 1015 ng/ml respectively). Eating 300 grams of celery root cannot reach this dose, so it cannot induce phototoxic reactions.

In comparison, eating half a lemon a day only provides 28.25 g of coumarin, or 0.02825 mg. To achieve photosensitivity, you would have to eat at least 353 lemons. So some people ask: How much do you need to eat to become photosensitized? My answer is: Eat until you die of photosensitivity. I don't know how many lemons you need to eat before you die of the sourness, but I think I would almost die if I ate two.

When it comes to coumarin content, grapes contain more than twice as much as lemons. If the saying that you can't touch lemons during the day is true, then, my dear friends, you should also eat grapes in the middle of the night! Well, in short, regarding the issue of drinking lemon water during the day, from the perspective of dosage, please rest assured.

2. Sun exposure problem

Another condition for photosensitivity is sufficient light exposure. For office workers, the possibility of being exposed to large amounts of sunlight is actually very low. Therefore, even if they eat 353 lemons, I don’t think they will have a photosensitivity reaction just sitting in the office (this can be calculated, the exposure is 25J, and the general UVA radiation intensity in the office is only around 15J, so it takes 353 hours of exposure).

Lemon is often blamed for the sayings that you can’t drink lemon water during the day, you can’t drink lemon water when sunbathing, and you will get darker if you drink lemon water and sunbathe. We still need to protect ourselves from the sun even if we don't drink lemon water. We will still get tanned even if we don't drink lemon water. Focusing on lemon water instead of sunscreen is completely putting the cart before the horse. Of course, photosensitive skin is sensitive to light, and it will remain photosensitive even if you don't drink lemon water. You may become more sensitive after drinking it, so you should wear sunscreen no matter what.