There are many different oils out there but when relating to beauty, skin care and aromatherapy there are the two you hear about and those are, essential oils and carrier oils.

What are Carrier Oils? 
Carrier oils are often used as a mixture to dilute the more potent essential oils. Most carrier oils are extracted from plants and have little to no aroma. Often, carrier oils also have benefits of their own (for example coconut oil is a great moisturizer) and can be matched with specific essential oils for added benefits when applied to skin. 
The most common carrier oils are olive oil, coconut oil, sunflower oil, and grapeseed oil. Other less common (and more expensive) carrier oils are argan oil, jojoba oil and emu oil.  
You must however, be aware of your own skin as some of these carrier oils come from nut based plants and could cause swelling of your skin if you have allergies. So we say most often the best non allergic and most basic carrier oil known is usually the grapeseed oil. It is also a very light oil which will rub into skin quicker and much deeper that’s why you will see most beauty therapists use it as the main massage oil when visiting a salon.

What are essential oils
An essential oil usually is the oil that carries a scent/fragrance from the plant that they were extracted from. Although they are not 'oily' really hence they are required to be diluted with some other medium, being water or carrier oil.
They are extracted most often through the use of distillation and stem form the non seed part of the plant.
The extraction process used to get the oils are usually different, but there are many exceptions. 
Essential oils are typically extracted by a method called, steam distillation, cold pressing or solvent extraction. But steam distillation is the most common. 
The common essential oils that are used are, lavender, peppermint, grapefruit, orange, lemongrass and so on. 
People can also use essential oils as a form of medicine for flu and sinus problems, for sleep, relaxation therapies and even for room perfumes/mists when diluted with water. 

There are many types of henna powders out there. For henna to be used on the skin, you must use fresh high-quality body art quality henna also known as BAQ. It must have gone through testing processes and be certified so as not to cause any skin irritations.
Commonly used is henna to dye the hair. It is usually a different quality henna powder.
 
There are a variety of henna out there, some which have had quite bad news about them. Especially ready made ones. You may even find that some of the other henna powders out there are too good to be true. You see all the instagram posts about how dark the stain is etc and when you buy it yourself you find that when you try it yourself it is not as dark as theirs! Well, there are many factors to be considered for this,
It could be that their skin tone is different so please dont compare yourself to theirs.
Sometimes the henna artists will mix the blend with other powders known as ‘mixing the blend’ and ofcourse the henna is usually left on for a longer time period.
 
So to be extra safe incase of anyone having alergies out there, please make sure they have passed factory tests and gained relevant certificates (you can find out this by looking at the labels they have displayed) and always do patch tests everytime you use a new henna even if its one youve been using for a long time because its a scientific fact that your skincells replace themselves every 2/3 weeks so your new skin could have a different reaction especially to a new/old harvest of henna.
 
How to darken a henna stain the honest way.
If you yourself choose to darken the henna stain (as not everyones skin colour is the same) then there are many ways which we will come to at a later stage. For quick measures you could also add other plants to it but since you're doing it, atleast you know what has been inside it! just make sure thats the only plant thats in the packet and again not mixed with something else. 
 
Why do people add sugar when making henna paste?
Sugar...
Well, adding sugar to your henna powder makes the henna stay wet against the skin longer, stick to the skin better, and makes the henna more stringy. It also helps add to darken the colour.

The role of water or lemon juice  
In order to get the best stain from organic fresh henna, you need to mix it with either water or lemon. People even use tea!
Lemon juice is acidic which allows the lawsone dye to be released from the henna slowly.
Both methods are fine but water releases stain quicker in the organic henna powder where as lemon juice and tea takes abit longer to release dye.
 
Oils for henna 
Both lavender and tea tree oils have monoterpene alcohols (also known as terp) This helps release more of the lawsone dye in the henna leaves resulting in a darker stain. Adding lavender oil also adds a lovely relaxing scent to your henna and keeps your henna paste from expiring. Essential oils are very potent and strong. You should just stick to using the minimum amount of oil you need to create a good mix. Never add more than 1 ounce (30 mL) of oil per 100 grams of henna. Lavender oil is usually the most safest option for pregnant women aswell. Always read the labels before use though. ​

How henna powder is made.
 
Henna plant grows in semi-arid zones and tropical areas. It produces the most dye when grown in temperatures between 35 and 45 °C (95 and 113 °F).
 
Once the henna leaves are harvested, they are set out to dry in the sun.
The dust, twigs etc are removed from the leaves before they are grinded. Bags of dried henna leaves are then taken to grinding machines and kept in a temperature controlled environment for best results where the henna powder is cleaned from its impurities. This process is repeated until a hygienic silk smooth powder is obtained which is safe use on skin. The powder quality is re-checked and finally approved. It is then packaged and shifted to the warehouse where it is exported globally. ​