According to Broken Secrets, fingernails and toenails grow faster in the summer because people are exposed to more daylight then. In daylight, the human body produces more vitamin D, which is essential for healthy growth in nails and hair. Cold environments and smoking can slow nail growth.
People also tend to drink more water in summertime, flushing out toxins so nails can grow stronger. Fingernails grow faster on the dominant hand because of better blood flow. The middle finger tends to grow the fastest, whereas the thumb and little finger grow most slowly. Fingernails grow as fast as toenails. The nails of youths grow faster than those of older individuals. Middle-aged people tend to have strong nails due to healthy eating choices and performing less manual work that would break the nails.
Since the 1930s, the speed of fingernail and toenail growth has increased by nearly a quarter, according to the Daily Mail. Studies at the University of North Carolina and Oxford University reveal that the nail on the big toe grows at a rate of over 2 millimeters per month, compared to 1.65 millimeters in the 1930s. This is attributed to modern-day diets, which are rich in protein from fish, meats, eggs, and poultry. Omega-3 is beneficial for cell structure, making nails less likely to break.