18K gold’s biggest advantage is its purity. As the purest form of gold that’s practical to use in an engagement ring, an 18K gold ring offers the gorgeous appearance of near-pure gold with most of the practical benefits of an alloy.
This extra purity can be especially obvious with 18K yellow or rose gold, which tends to show a warmer, more vibrant tone in 18K than in 14K gold.
The higher purity level of 18K gold also makes it less likely to trigger skin allergies than 14K or 10K gold. Although 18K gold still contains nickel and other alloy metals, they’re only present in small quantities, making the risk of contact dermatitis or other allergic reactions very small.