Contrary to urban legend, writing on skin with an ink pen does not cause ink poisoning. Common ink pens are almost entirely non-toxic. The basic components of pen ink are solvents, dyes, pigments and water. More than 1 oz. of the fluid would have to be ingested orally in order to significantly affect or poison a person---difficult to accomplish with only an ink pen. However, printer cartridge ink contains the slightly toxic pigment component P-Anisidine.
It should be noted that tattoo ink, while mildly irritative under some circumstances, is non-toxic when tattooed into the skin (although it can be hazardous if ingested).
The most common symptoms of exposure to ink, whether from a pen, bottle or cartridge, are eye irritation and the staining of skin and mucous membranes.
Perhaps most at risk for ink poisoning are workers in the printing business who are constantly exposed to ink and solvents. Excessive exposure to the chemical ingredients in ink can cause long-term skin problems. Screen printers, for example, may occasionally be splashed with ink during the printing process.
Symptoms that occur after ink is ingested may include severe headaches, irritation to the exposed area and damage to the nervous system.
In the case of workers exposed to ink over time, long-term effects can be dermatitis and skin sensitization. Solvents break down the natural oils found in our skin, removing them and leaving the skin without protection. Without oils, the skin becomes overly dry, sensitive and easily irritated.
Because ink is mostly non-poisonous, mild external exposure can be treated at home by simply rinsing the affected area (eyes or skin) with water.
If ink is swallowed, immediately contact the National Poison Control Center at (800) 222-1222. This is a 24-hour, 7-days-a-week phone number---it doesn't have to be an emergency to call. A representative will recommend the best course of action, but if in doubt immediately seek medical care.
For those in the printing industry, take the precautions necessary to prevent long-term damage. Work in a well-ventilated area, wear gloves and impervious clothes such as an apron, and clean your work area often.