By Al-Alamah, Al-Faqeeh Abdur Rahman ibn Nasr Al-Barrak (may Allah preserve him)
Question: What is the verdict on wearing artificial fingernails and eyelashes? Is this act considered among the acts of joining false hair with real hair?
Answer: Adding synthetic fingernails disagrees with the sunnah and (fitrah) natural disposition. The Prophet (peace and blessings be upon him) said,
خمس من الفطرة
There are five things among the Fitrah
Following these words, he (peace and blessings be upon him) mentioned clipping the fingernails. Also He (peace and blessings be upon him) mentioned when the nails must be clipped; and that they shouldnýt grow unclipped beyond forty days. Intentionally extending the fingernails causes a person to resemble an animal or disbeliever. This act is disfeaturing for a woman and not beauty. When a woman adds fake nails this shows she has a corrupt fitrah and decreased intellect.
Similarly, adding synthetic eyelashes resembles the disbelievers and is among the acts of joining false hair with real hair. I consider both of these actions to be impermissible. And Allah knows best.
Taken from: http://albarrak.islamlight.net/index.php?option=com_ftawa&task=view&id=31346&catid=&Itemid=35
Translated by: Abu Aaliyah Abdullah ibn Dwight Battle
Doha, Qatar 1430 H