Infections are rare but can occur so it is important to be mindful to look and notice anything that may indicate the beginning of an infection. Signs of an infected tattoo can be seen as soon as 2 days after getting a tattoo. It is normal to have some swelling and redness around your tattoo for up to 48 hours. After that time, the pain, redness, swelling should be getting better. If you experience increased pain, swelling and/or redness, that may be a sign of infection.
There are several common types of pathogens that can cause an infection such as Staphylococcus (Staph) (which is the most common), Streptococcus and Methicillin-Resistant Staphylococcus aureus (MRSA) to name a few (and yes there are other pathogens out there that can also cause an infection, but I won't bore you with this). But what I will tell you is that it is important to identify an infection as it can become serious quickly.
Other signs are listed below.
Signs of an infected tattoo:
fever, chills, shivering
increased swelling of the tattooed area
increased warmth over the tattoo
pus (an exudate of white-yellow, yellow or yellow-brown)
increased redness, bumps or red streaks
areas of hard, raised tissue
blisters
Most importantly, if you are not sure if your tattoo is infected but notice a change that is concerning, contact your tattoo artist or seek medical care at once. Delaying getting treatment can be serious.