Sitting under a parasol may give you partial sun protection; however, they do not protect you from sunburn. Parasol may block the sun overhead but does not provide any shade on your side when you are walking in an outdoor area facing west or east. Moreover, they scatter the sun's rays in all directions instead of concentrating them accidentally in one direction.
It's important to note that parasols do not block UVA rays and can't be used as a substitute for sunscreen. For maximum protection, it is best to alternate between using a parasol or an umbrella with broad coverage and applying a generous amount of broad-spectrum sunscreen.