Safety considerations: Expressed Lemon essential oil is phototoxic.
Tisserand and Young recommend a dermal maximum use at 2.0% to avoid the risk of a phototoxic reaction. If applied to the skin at over maximum use level, skin must not be exposed to sunlight or sunbed rays for 12 hours.
[Robert Tisserand and Rodney Young, Essential Oil Safety (Second Edition. United Kingdom: Churchill Livingstone Elsevier, 2014), 87, 330-331.]
Lemon essential oil, like all citrus peel essential oils with high content of (+)-limonene, can oxidise easily. We recommend that you store the bottle in a fridge and never use old, oxidised oil to avoid skin irritation.