Are essential oils safe for our skin?

What are they?
Essential oils (EOs) are the volatile essences of plants. They can be extracted from any plant part. No matter the source, these oils are complex mixtures, some good for skin, others not so good.
The volatile fragrant portion of plants is what makes essential oil for skin problematic or beneficial.
It’s all about where the essential oil is sourced from and the quantity of it used.
How Essential Oils can hurt our skin?
The only difference between a toxin and a medicine is its dosage. Some people have died of excessive water intake. So, if used in amounts too high EOs can become harmful too. 
Like anything in this world, there are some people allergic or reactive to essential oils. And yes for those people who have extremely sensitive skin and/or skin issues, yes, EO’s should be avoided at first to find out what is going on with the skin. I personally suffer from sensitive and extremely reactive skin but never had a problem with the essential oils I safely formulate in my products (or with other well known natural skincare brands that I trust).
In general, some components of essential oils are indeed beneficial for skin helping with conditions like acne or skin ageing. But other components can be irritating, cause allergic reactions and even photodamage.
So how can we know if an essential oil is good or bad for our skin?
The answer is trust. How much do you trust the skincare brand product you just bought? In my opinion, it is essential that any skincare formulated with EOs be done so by formulator(s) who are professionally trained.
According to IFRA (Iternational Fragance Association) website, In 1973 the global fragrance industry came together to form a new international association. Its mission: to represent the collective interests of the industry and promote the safe use and enjoyment of fragrances around the world.
Skincare professionals work around a list of what is called ‘’essential oils sensitiser limits’’, standards defined by IFRA. This is a list of the different ‘’bad components’’ (eg limonene, farnesol, eugenol…) that can be found in an essential oils and the limit amount you can use in order to avoid (any) reaction. So for example, once I get the technical sheet sheet from the supplier I ordered the essential oil from, I check which sensitisers it contains and calculate how much of each sensitiser are there in total in my product. Once I have the amount, I see if it is above the limit given by IFRA or not and calculate again how much of the essential oil or blend of essential oils I can use safely in my product. This, which is already complicated, is even more time consuming when you use more than one essential oil (like me) in you final products.
Apart from this, certain essential oils, like for example lemongrass, are even more regulated and have its own topical limits as they can produce different skin reactions.
As you can imagine, calculate the ratio of effective yet safe amount of essential oils in each skincare product is a nightmare for any skincare formulator. That is one of the reassons why some important companies have decided not to use them at all. Essential oils are expensive, risky when not used correctly, time consuming and, like other ingredients, (like parabens, silicones, etc that some companies proud of being essential oil free formulate with) could do more damage than good.
Claiming that a given company is essential oil free is purely a marketing strategy. Pure, organic essential oils formulated professionally assist the skin in proper function and health. They must be used at specific concentrations, be pure, organic and unadulterated, manipulated by a professional and they must not be past their shelf life.