Choose a fresh, organically grown cucumber. It is very important to use only pesticide-free cucumbers. Choose a cucumber with dark green skin, with no signs of yellowing. Active ingredients in different varieties of cucumber are the same, so you can take any of them. Avoid waxed cucumbers, they are probably not as fresh as you want. One small or medium-sized cucumber is enough because its juice cannot be kept more than 24 hours. Wash the cucumber, and slice, grate or blend it in the food processor. It is entirely up to you whether you will use it with skin or peel it off.
Leave it for 10-15 minutes to release the juice, then squeeze it with clean hands (if it is sliced), or strain it using a clean cloth to separate small particles and seeds. Finally, collect the juice.
Use a cotton ball to apply cucumber juice on the skin and leave it for 10-15min, then rinse it with lukewarm water. Another way of application is to leave it on the skin without rinsing. You can repeat this procedure several times a day.
Always use freshly prepared juice. You can keep it fresh in the refrigerator for no more than one single day. Since it is raw, unprocessed and free from any preservatives, it is highly sensitive/prone to bacterial and fungal spoilage and deterioration by naturally-occurred enzymes. This is also a reason why you should never incorporate raw cucumber juice (or any other raw, unpreserved herbal juice or puree) into your cosmetic preparations if you want them to last longer than one day.
If you want to preserve your cucumber juice to last longer than one day, you can mix it with alcohol (final mixture should contain no less than 15% of pure ethanol), or boil it and add cosmetic-grade preservative. In any of these cases, your cucumber tonic is no longer the same as the raw one, and its properties and skin effects are different.
In general, cucumber is considered to be non-irritant to the skin, but some people can be sensitive to it. Cucumber can cause allergy, usually with symptoms in the mouth and pharyngeal area. It usually indicates an allergy to all members of the gourd family (like watermelons, zucchini, cantaloupes, pumpkins and others). Cucumber allergy (as well as to other gourds) is associated with ragweed allergies because the proteins in the cucumber are very similar to those present in ragweed pollen, so that the body misidentifies them. Since persons who suffer from ragweed allergies may cross react with cucumber, they are recommended to avoid any form of raw cucumber.