Shaykh Muhammad ibn Saalih al-Uthaymeen rahimahullaah was asked the following question:
Q: O noble Shaykh! What is the ruling on having one’s ears pierced with more than one piercing – for the purpose of wearing gold -; so that she (the woman) can wear more than one earring in one ear?
A: I fear that this is from extravagance – that a woman places in her ears more than that which is the custom. And Allaah has said:
وَكُلُوا وَاشْرَبُوا وَلَا تُسْرِفُوا ۚ إِنَّهُ لَا يُحِبُّ الْمُسْرِفِينَ
And eat and drink, but be not excessive. Indeed, He likes not those who are extravagant. [7:31]
So if the custom was that a woman had two piercings in one ear – then there is no harm (in that).
However if that was not the custom, then it is counted as being from the blameworthy extravagance.
And it is feared that the women would compete and show-off with regards to that. So one year she will have two piercings in each ear, and the next year she will have three or four piercings – until she pierces all of her ear. And this (occuring) is not something far-fetched; as the women they emulate one another.
[Source: Shaykh Muhammad ibn Saalih al-Uthaymeen rahimahullaah official website: http://www.binothaimeen.com/sound/snd/a0015/a0015-45b.rm – voice clip from 5:15 mins – 6:28 mins]