A wetness sensor for an absorbent article that is formed from an ink is provided. The ink includes a proton-accepting chromogen and a proton-donating agent (or color developer). Prior to use, the ink is generally dry and in a protonated form so that it has a visible color. However, upon contact with bodily fluids {e.g., urine, fecal matter, mucus, menses, vaginal fluid, etc.), water in the fluid can lead to deprotonation of the chromogen, thereby resulting in a shift of the absorption maxima of the chromogen towards either the red {"bathochromic shift") or blue end of the spectrum ("hypsochromic shift"). To increase the rate of the color change during use, the present inventors have discovered that a specific type of proton-donating agent may be employed. More particularly, the proton- donating agent is an aliphatic carboxylic acid that is highly soluble in the bodily fluid (e.g., urine), and therefore results in a color change that is very rapid and may be detected within a relatively short period of time. The extent of the color change is also generally sufficient to provide a "real-time" indication of wetness on the absorbent article.
