Should they be? This is completely up to an individual's preferences and as you get to know your own skin and the perfume you’re using, you’ll start to understand what works for you and what doesn’t.
Of course, like everything, there are advantages and disadvantages to using synthetics in perfume, which is the same as using all-natural ingredients.
If perfumers are using a new molecule that has little experience within the market, although deemed safe now it could be considered unsafe in the future. Some synthetic ingredients may have biodegradability issues that may not come to light for a few years after their approval.
However, in many cases, ingredients synthesised in labs are less harmful than natural ones for a range of different reasons, such as overharvesting for Sandalwood.
Synthetics can be modified to ensure there are minimal allergens such as Oakmoss. As a vegan-friendly company ingredients such as ambergris which is produced in the whale's digestive system has to be replaced with a synthetic alternative, this is becoming very popular in modern times and it is not uncommon for perfumes to contain more than 50% synthetic ingredients.
Overall, we have to accept that sometimes lab-made is more environmentally friendly than naturally derived ingredients.