The refreshing smell of lemons may be one of the most recognizable scents and yet is one of the most under-utilized essential oils. Lemons are so common in beverages, cooking, candy, and cleaning products that is easy to overlook its benefits as an essential oil.
What is the history of Lemon Essential Oil?
The lemon (Citrus x limon or Citrus limon) is a member of the plant genus Citrus. Citrus plants are flowering plants belonging to the family Rutaceae and include the other well-known citrus fruits, such as oranges, grapefruit, limes, tangerines, pomelos, and citrons. Lemon trees can both flower and produce fruit at the same time.  The name lemon comes from the Old French limon, Italian limone, Arabic limun, and Persian limun which are all generic names for any citrus fruits .
The Citrus species has 3 ancient branches from which the modern fruits descended: Citrus medica (citrons), Citrus reticulata (mandarins), and Citrus maxima (pumelos).  The entire family of citrus fruit evolved from a common ancestor 15 million years ago and then split into two groups about 7 million years ago. Almost all of the citrus fruit we have today is descended from the 3 varieties, or cultivars, as hybrids in the last several thousand years. 
- Assam: The true origins of the lemon is unknown but is believed to have grown originally in Assam of northeast India or China or Burma.
- Rome: Lemons made their first entrance into Rome in the second century AD.  The Roman author Pliny the Elder appears to reference the citron, referring to it as “medicinal fruit” in his book Pliny’s Natural History 
- Arabia: The first description of the lemon as we know it was made in the early 10th century by Qustus al-Rumi 
- Persia: The lemon was introduced in approximately 700 AD 
- Iraq: Like Persia, the lemon first made its way into Iraq in approximately 700 AD 
- Egypt: Like Persia and Iraq, the lemon was presumed to have been introduced by 700 AD 
What are the most common types of lemon?
The common lemon is a hybrid of a citron and a sour orange  There are many varieties of lemon because they cross-pollinate easily.
- Common supermarket variety
- Grows year-round
- Also known as “Four Seasons” because it produces fruit and flowers throughout the year
- A variety of the Eureka lemon is a variegated green and yellow skin with pink fruit inside 
- High level of acidity 
- Similar to Eurkea variety
- Rougher skin than Eureka variety (if produced in the Mediterranean)
3. Meyer Lemon
- Citrus x meyeri
- Named after Frank N. Meyer, the American agricultural explorer who brought the variety to the U.S. from China
- Native to China
- A hybrid between a citron and a mandarin/pomelo
- Rounder shape than other lemons
- Sweeter and less acidic flavor than Eureka varieties
- Mostly grown in California; however, in the 1940's the trees were symptomless carriers of a dangerous virus and most of the Meyer Lemon trees in the U.S. were destroyed. The University of California engineered a virus-free variety in 1975 called the “Improved Meyer Lemon” (Citrus x meyeri ‘Improved’ 
- A hybrid of lemon, mandarin, and orange tree 
- Does not have a characteristic “lemon” smell 
4. Bonnie Brae
- Grown mostly in San Diego County, U.S. 
5. Femminello St. Theresa or Sorrento
- Traditionally used in making the lemon liquor limoncello
- Native to Italy
- Zest (skin of fruit) is high in oils 
6. Yen Ben
- Variety cultivated in Australasia 
What is an essential oil?
Aromatic plants have secondary metabolisms (a natural defense mechanism against bacteria and pests). These defense mechanisms can be strong smells, colors, or attractants for pollinators. Essential oils represent the essence of a plant.
How is Lemon Essential Oil made?
Citrus essential oil is made from cold-pressing, but in general, essential oils can be made through distillation with steam, mechanically expressed, or extracted with a solvent. Some solvents commonly used for extraction are hexane, ethanol, or acetone. After the essential oil is extracted, it is very concentrated.
Despite being called oils, essential oils do not contain any fats (lipids) and are not actual oils. Instead, they are comprised of very volatile compounds with many complex constituents. Some compounds can have anywhere from twenty to sixty constituents. The constituents can be structured into two groups: aromatic compounds and terpenes. The actual composition of the constituents and the ratio of terpenes to aromatic compounds depends on the plant. 
- Cold Pressed Expression:
Citrus fruits undergo cold pressing expression to extract their oils. It was originally performed by hand and was expressed through pressing sponges. The skin (or zest/rind) was pressed with a sponge to absorb the oil, and once the sponge was full of oil, it was then pressed into a container. It would then be left to let the essential oil separate from the water or juice and the essential oil would then be taken off the top. 
- The second method of cold-pressed expression that is less time-consuming and has become common during modern production of citrus essential oils is “Écuelle à piquer”. During the extraction, the rind of the fruit is punctured in a container with spikes and rotated, releasing the essential oil into a container below. The rotation used is centrifugal force from spinning in a centrifuge, and the fast spinning separates most of the oil from the fruit juice. 
Citrus oils that have been collected through cold-pressed expression contain small amounts of residues, including waxes, and the cold process leaves the aroma of the peel of the fruit retained inside the oil. 
Though not as popular, citrus oils can be distilled from the whole fruit or its peels. It does not have the same aroma as citrus that has been cold pressed, but they are often purer and do not contain any residues. The advantage to not containing the residues means that when the essential oil is used in a diffuser it doesn’t clog as easily, and it is less likely to stain clothes and fabric. Distilled citrus oils are less likely to be photosensitizing agents because they do not contain compounds called nonvolatile furocoumarins. 
Why is Lemon Essential Oil a photosensitive essential oil?
Furocoumarins are organic chemical compounds that are used as a defense mechanism to ward off pests and predatory animals. They are present in many citrus plants and are generally left in the essential oil after cold pressed extraction. They can increase photosensitivity: a skin irritation that is caused by these chemical compounds when you combine the oils with exposure of your skin to sunlight.
The recommended course of action when using a photosensitizing essential oil is to avoid sunlight and all UV lights (including tanning beds) for about 12-18 hours after the essential oil has been applied to skin or to apply to essential oil to the skin in the evening before bed. Some essential oils are labeled “FCF” which means they have undergone a separate process after extraction when the distilled essential oil is heated to destroy the furocoumarins. 
Some common photosensitive citrus essential oils include:
- Lemon (Citrus limon)
- Lime (Citrus medica)
- Grapefruit (Citrus paradise)
Some members of the Citrus family which are not photosensitizing include:
- Red Mandarin (Citrus nobilis)
- Tangerine (Citrus reticulata)
- Sweet Orange (Citrus sinensis)
- Blood Orange (Citrus x senensis) 
What is Lemon Essential Oil made of?
The lemon fruit consists of the peel, fruit pulp, and juice. All varieties of lemon contain acids, limonoids, citrus oils, coumarins, bioflavonoids, and terpenes; and the fruit contains polysaccharides and oligosaccharides (sugars). Lemons contain more acid than any other fruit in its citrus family. Acidity is determined by the malic acid and citric acid content. 
The fruit of the lemon contains:
- 4-4.38% citric acid
- 07-0.26% malic acid
- Together, the overall acidity of lemon is 3.5-6% 
The fruit pulp contains sugars, polysaccharides, and oligosaccharides, with about 50% polysaccharides and 40% sugars. The amount of sugar contained in lemon juice varies depending on where the fruit was produced; the juice from Californian lemons has 0.81-3.2% sugar, whereas the juice from Floridian lemons contains 3.7% sugar.
- The polysaccharides include:
Pectin, galacturonan, glucan, arabinan, and xylan 
Depending on the ripeness of the fruit, the bioflavonoid composition may be different. For instance, some research concluded that unripened lemons contain mostly hesperidin, versus ripened lemons which contain demethylated hesperidin (eriodictyol). Other research concluded that eriodictyol is the primary bioflavonoid regardless of stage of ripeness. Fresh lemon juice contains 0.046-0.12% hesperidin but juice with pulp contains higher amounts of hesperidin. 
- The bioflavonoids include:
Diosmin, hesperidin, eriodictyol, neohesperidoside, eriodictyol glycoside, naringenin, neodiosmin, chyrsoeriol, rutinoside, isorhamnetin, limocitrol, lnocitrin, isolimocitrol, and others. 
The primary monoterpene present in lemon juice is limonene. Along with limonoids and lemon flavonoids, limonene gives lemon its characteristic aroma and flavoring.
Lemon oil contains several coumarins in both the oil, peel, and juice.
- The coumarins of lemon essential oil include:
Bergapten, imperatorin, oxypeucedanin, 8-geranyloxypsolaren, phellopterin, isopimpinellin, 5-geranyloxy-8-methoxypsoralen, and others 
- The coumarins of lemon peel and lemon juice include:
8-geranyloxypsolaren, 5-geranyloxy-7-methoxycoumarin, bergamottin, citropten, and oxypeucedanin 
How to Use Lemon Essential Oil
Essential oils are very strong and must be mixed with a carrier oil so they will be diluted. Be sure to use a diluted essential oil blend unless instructed by your healthcare practitioner to do otherwise. Using essential oils in children have specific rules and should be supervised by a healthcare practitioner.
The benefits of essential oils can be experienced through topical application or aromatherapy and are not usually taken internally unless under the guidance of an aromatherapy practitioner.
Safety and Side Effects of Lemon Essential Oil
The main side effect of lemon essential oil is its photosensitive properties. Sunlight, UV light, and tanning beds should be avoided for 12-18 hours after topical application. 
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