The answer to this question actually depends on several factors. In order to understand this, it is helpful to understand what a sickle cell is, and where it comes from. A sickle cell is simply a red blood cell that has an abnormal elongated (sickle- or banana-like) shape due to its possession of hemoglobin that was not constructed properly. This construction error occurs because of a mutation in a gene that plays a part in directing the hemoglobin assembly-- that is, the hemoglobin gets constructed wrong because there is a mistake in the blueprint instructions for how to build it. So, a sickle cell is really just a red blood cell that, because it contains one faulty part, ends up having a different shape.

What would happen if one of these cells somehow got into your blood stream? Well, probably nothing, actually. The sickle cell is not really dangerous or harmful-- it does not release any toxins, or destroy other cells, or even interfere with your normal bodily functions. However, while it is theoretically possible for you to have one sickle cell in your body (say by a blood transfusion), the reality is that either your body produces proper red blood cells (in which case you wont have any sickle cells) or it produces sickle cells (in which case you will have a lot of sickle cells). While a single sickle cell is dangerous, having a lot of sickle cells in your blood can cause problems!

Normal red blood cells are round (kind of like a donut, but with just a depression instead of a hole in the middle) and smooth. This shape is perfect for them to accomplish their task of drifting easily through the blood vessels carrying oxygen to your body. They just flow smoothly, bumping off the sides and around anything else they encounter, kind of like an inner tube on a stream. However, because sickle cells have an elongated more jagged shape, they flow more like a canoe or a kayak than an inner tube: they are more likely to get stuck when they run into something. So, when a normal red blood cell enters a very narrow capillary, it will just flow right through, but a sickle cell is more likely to go in sideways and get stuck because it does not fit very well. When a lot of sickle cells are present a huge logjam of stuck cells can result!

Such a blockage prevents the proper flow of oxygen-carrying red blood cells into the capillary, and as a consequence that part of the body does not receive the oxygen it needs. When an organ does not receive enough oxygen it can be damaged or even die, so this is a serious problem. Imagine if your liver, heart, or brain were to become damaged or die! Therefore, people whose bodies produce sickle cells can suffer from these blockages, which are painful and also can cause major health problems or even death.

How bad of a problem this is depends on how many of the sickle cells are produced in the body. In our DNA we all have two copies of every gene: one from our mother, and one from our father. If a person receives a normal copy of the key hemoglobin construction gene from both parents, that persons body has two good hemoglobin blueprints and will only produce normal cells. In that case, sickle cells will never be a problem. However, if a person receives a normal copy from one parent but a sickle copy from the other parent, that persons body will have one of each kind of blueprint and will therefore produce both types of cells. In this case, the sickle cell problem is not very great since a lot of the red blood cells are normal, but occasionally the sickle cells can cause blockages to occur resulting in a health crisis. This kind of problem is more likely to occur during periods of exercise, when blood flow and the bodys oxygen demands are higher, or when the body is dehydrated, resulting in generally poorer blood flow. Finally, if a person receives a bad copy of the gene from both parents, that persons body will produce only sickle red blood cells. In this case, the blockage problems are likely to be frequent and severe.